diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index a24367c8..a4f85ea2 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -86,6 +86,12 @@ jobs:
         command:  check
         args: --features attributes
 
+    - name: build unstable only
+      uses: actions-rs/cargo@v1
+      with:
+        command:  build
+        args: --no-default-features --features unstable
+
     - name: tests
       uses: actions-rs/cargo@v1
       with:
diff --git a/Cargo.toml b/Cargo.toml
index a5b5c4f0..8c890125 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -24,12 +24,15 @@ rustdoc-args = ["--cfg", "feature=\"docs\""]
 [features]
 default = [
   "std",
+  "async-executor",
+  "async-io",
   "async-task",
+  "blocking",
+  "futures-lite",
   "kv-log-macro",
   "log",
   "num_cpus",
   "pin-project-lite",
-  "smol",
 ]
 docs = ["attributes", "unstable", "default"]
 unstable = [
@@ -54,7 +57,7 @@ alloc = [
   "futures-core/alloc",
   "pin-project-lite",
 ]
-tokio02 = ["smol/tokio02"]
+tokio02 = ["tokio"]
 
 [dependencies]
 async-attributes = { version = "1.1.1", optional = true }
@@ -77,7 +80,10 @@ futures-timer = { version = "3.0.2", optional = true }
 surf = { version = "1.0.3", optional = true }
 
 [target.'cfg(not(target_os = "unknown"))'.dependencies]
-smol = { version = "0.1.17", optional = true }
+async-executor = { version = "0.1.1", features = ["async-io"], optional = true }
+async-io = { version = "0.1.5", optional = true }
+blocking = { version = "0.5.0", optional = true }
+futures-lite = { version = "0.1.8", optional = true }
 
 [target.'cfg(target_arch = "wasm32")'.dependencies]
 futures-timer = { version = "3.0.2", optional = true, features = ["wasm-bindgen"] }
@@ -87,6 +93,12 @@ futures-channel = { version = "0.3.4", optional = true }
 [target.'cfg(target_arch = "wasm32")'.dev-dependencies]
 wasm-bindgen-test = "0.3.10"
 
+[dependencies.tokio]
+version = "0.2"
+default-features = false
+features = ["rt-threaded"]
+optional = true
+
 [dev-dependencies]
 femme = "1.3.0"
 rand = "0.7.3"
diff --git a/src/fs/file.rs b/src/fs/file.rs
index 2ff5643e..56d292b9 100644
--- a/src/fs/file.rs
+++ b/src/fs/file.rs
@@ -315,7 +315,7 @@ impl Drop for File {
         // non-blocking fashion, but our only other option here is losing data remaining in the
         // write cache. Good task schedulers should be resilient to occasional blocking hiccups in
         // file destructors so we don't expect this to be a common problem in practice.
-        let _ = smol::block_on(self.flush());
+        let _ = futures_lite::future::block_on(self.flush());
     }
 }
 
diff --git a/src/net/tcp/listener.rs b/src/net/tcp/listener.rs
index 09f5812f..8c87fc5f 100644
--- a/src/net/tcp/listener.rs
+++ b/src/net/tcp/listener.rs
@@ -2,7 +2,7 @@ use std::future::Future;
 use std::net::SocketAddr;
 use std::pin::Pin;
 
-use smol::Async;
+use async_io::Async;
 
 use crate::io;
 use crate::net::{TcpStream, ToSocketAddrs};
@@ -81,7 +81,7 @@ impl TcpListener {
         let addrs = addrs.to_socket_addrs().await?;
 
         for addr in addrs {
-            match Async::<std::net::TcpListener>::bind(&addr) {
+            match Async::<std::net::TcpListener>::bind(addr) {
                 Ok(listener) => {
                     return Ok(TcpListener { watcher: listener });
                 }
@@ -227,7 +227,7 @@ cfg_unix! {
 
     impl IntoRawFd for TcpListener {
         fn into_raw_fd(self) -> RawFd {
-            self.watcher.into_raw_fd()
+            self.watcher.into_inner().unwrap().into_raw_fd()
         }
     }
 }
@@ -251,7 +251,7 @@ cfg_windows! {
 
     impl IntoRawSocket for TcpListener {
         fn into_raw_socket(self) -> RawSocket {
-            self.watcher.into_raw_socket()
+            self.watcher.into_inner().unwrap().into_raw_socket()
         }
     }
 }
diff --git a/src/net/tcp/stream.rs b/src/net/tcp/stream.rs
index 63232fa3..f7bd5c91 100644
--- a/src/net/tcp/stream.rs
+++ b/src/net/tcp/stream.rs
@@ -2,7 +2,7 @@ use std::io::{IoSlice, IoSliceMut};
 use std::net::SocketAddr;
 use std::pin::Pin;
 
-use smol::Async;
+use async_io::Async;
 
 use crate::io::{self, Read, Write};
 use crate::net::ToSocketAddrs;
@@ -77,7 +77,7 @@ impl TcpStream {
         let addrs = addrs.to_socket_addrs().await?;
 
         for addr in addrs {
-            match Async::<std::net::TcpStream>::connect(&addr).await {
+            match Async::<std::net::TcpStream>::connect(addr).await {
                 Ok(stream) => {
                     return Ok(TcpStream {
                         watcher: Arc::new(stream),
diff --git a/src/net/udp/mod.rs b/src/net/udp/mod.rs
index d361a6fc..dd47e058 100644
--- a/src/net/udp/mod.rs
+++ b/src/net/udp/mod.rs
@@ -2,7 +2,7 @@ use std::io;
 use std::net::SocketAddr;
 use std::net::{Ipv4Addr, Ipv6Addr};
 
-use smol::Async;
+use async_io::Async;
 
 use crate::net::ToSocketAddrs;
 use crate::utils::Context as _;
@@ -74,7 +74,7 @@ impl UdpSocket {
         let addrs = addrs.to_socket_addrs().await?;
 
         for addr in addrs {
-            match Async::<std::net::UdpSocket>::bind(&addr) {
+            match Async::<std::net::UdpSocket>::bind(addr) {
                 Ok(socket) => {
                     return Ok(UdpSocket { watcher: socket });
                 }
@@ -506,7 +506,7 @@ cfg_unix! {
 
     impl IntoRawFd for UdpSocket {
         fn into_raw_fd(self) -> RawFd {
-            self.watcher.into_raw_fd()
+            self.watcher.into_inner().unwrap().into_raw_fd()
         }
     }
 }
@@ -530,7 +530,7 @@ cfg_windows! {
 
     impl IntoRawSocket for UdpSocket {
         fn into_raw_socket(self) -> RawSocket {
-            self.watcher.into_raw_socket()
+            self.watcher.into_inner().unwrap().into_raw_socket()
         }
     }
 }
diff --git a/src/os/unix/net/datagram.rs b/src/os/unix/net/datagram.rs
index 52c6b07f..83ef9fe9 100644
--- a/src/os/unix/net/datagram.rs
+++ b/src/os/unix/net/datagram.rs
@@ -4,7 +4,7 @@ use std::fmt;
 use std::net::Shutdown;
 use std::os::unix::net::UnixDatagram as StdUnixDatagram;
 
-use smol::Async;
+use async_io::Async;
 
 use super::SocketAddr;
 use crate::io;
@@ -335,6 +335,6 @@ impl FromRawFd for UnixDatagram {
 
 impl IntoRawFd for UnixDatagram {
     fn into_raw_fd(self) -> RawFd {
-        self.watcher.into_raw_fd()
+        self.watcher.into_inner().unwrap().into_raw_fd()
     }
 }
diff --git a/src/os/unix/net/listener.rs b/src/os/unix/net/listener.rs
index a63bd4b6..078b780d 100644
--- a/src/os/unix/net/listener.rs
+++ b/src/os/unix/net/listener.rs
@@ -5,7 +5,7 @@ use std::future::Future;
 use std::os::unix::net::UnixListener as StdUnixListener;
 use std::pin::Pin;
 
-use smol::Async;
+use async_io::Async;
 
 use super::SocketAddr;
 use super::UnixStream;
@@ -217,6 +217,6 @@ impl FromRawFd for UnixListener {
 
 impl IntoRawFd for UnixListener {
     fn into_raw_fd(self) -> RawFd {
-        self.watcher.into_raw_fd()
+        self.watcher.into_inner().unwrap().into_raw_fd()
     }
 }
diff --git a/src/os/unix/net/stream.rs b/src/os/unix/net/stream.rs
index 74bd6aef..3b2fe36f 100644
--- a/src/os/unix/net/stream.rs
+++ b/src/os/unix/net/stream.rs
@@ -5,7 +5,7 @@ use std::net::Shutdown;
 use std::os::unix::net::UnixStream as StdUnixStream;
 use std::pin::Pin;
 
-use smol::Async;
+use async_io::Async;
 
 use super::SocketAddr;
 use crate::io::{self, Read, Write};
diff --git a/src/os/windows/mod.rs b/src/os/windows/mod.rs
index 6dac11b6..67bf0372 100644
--- a/src/os/windows/mod.rs
+++ b/src/os/windows/mod.rs
@@ -5,5 +5,6 @@ cfg_std! {
 }
 
 cfg_unstable! {
+    #[cfg(feature = "default")]
     pub mod fs;
 }
diff --git a/src/rt/mod.rs b/src/rt/mod.rs
index d8550aac..f58afb18 100644
--- a/src/rt/mod.rs
+++ b/src/rt/mod.rs
@@ -27,7 +27,7 @@ pub static RUNTIME: Lazy<Runtime> = Lazy::new(|| {
     for _ in 0..thread_count {
         thread::Builder::new()
             .name(thread_name.clone())
-            .spawn(|| crate::task::block_on(future::pending::<()>()))
+            .spawn(|| crate::task::executor::run_global(future::pending::<()>()))
             .expect("cannot start a runtime thread");
     }
     Runtime {}
diff --git a/src/task/builder.rs b/src/task/builder.rs
index 0024f8ab..236081c0 100644
--- a/src/task/builder.rs
+++ b/src/task/builder.rs
@@ -7,7 +7,7 @@ use std::task::{Context, Poll};
 use pin_project_lite::pin_project;
 
 use crate::io;
-use crate::task::{JoinHandle, Task, TaskLocalsWrapper};
+use crate::task::{self, JoinHandle, Task, TaskLocalsWrapper};
 
 /// Task builder that configures the settings of a new task.
 #[derive(Debug, Default)]
@@ -61,9 +61,9 @@ impl Builder {
         });
 
         let task = wrapped.tag.task().clone();
-        let smol_task = smol::Task::spawn(wrapped).into();
+        let handle = task::executor::spawn(wrapped);
 
-        Ok(JoinHandle::new(smol_task, task))
+        Ok(JoinHandle::new(handle, task))
     }
 
     /// Spawns a task locally with the configured settings.
@@ -81,9 +81,9 @@ impl Builder {
         });
 
         let task = wrapped.tag.task().clone();
-        let smol_task = smol::Task::local(wrapped).into();
+        let handle = task::executor::local(wrapped);
 
-        Ok(JoinHandle::new(smol_task, task))
+        Ok(JoinHandle::new(handle, task))
     }
 
     /// Spawns a task locally with the configured settings.
@@ -166,10 +166,10 @@ impl Builder {
             unsafe {
                 TaskLocalsWrapper::set_current(&wrapped.tag, || {
                     let res = if should_run {
-                        // The first call should use run.
-                        smol::run(wrapped)
+                        // The first call should run the executor
+                        task::executor::run(wrapped)
                     } else {
-                        smol::block_on(wrapped)
+                        futures_lite::future::block_on(wrapped)
                     };
                     num_nested_blocking.replace(num_nested_blocking.get() - 1);
                     res
diff --git a/src/task/executor.rs b/src/task/executor.rs
new file mode 100644
index 00000000..d9caf053
--- /dev/null
+++ b/src/task/executor.rs
@@ -0,0 +1,72 @@
+use std::cell::RefCell;
+use std::future::Future;
+
+static GLOBAL_EXECUTOR: once_cell::sync::Lazy<async_executor::Executor> = once_cell::sync::Lazy::new(async_executor::Executor::new);
+
+thread_local! {
+    static EXECUTOR: RefCell<async_executor::LocalExecutor> = RefCell::new(async_executor::LocalExecutor::new());
+}
+
+pub(crate) fn spawn<F, T>(future: F) -> async_executor::Task<T>
+where
+    F: Future<Output = T> + Send + 'static,
+    T: Send + 'static,
+{
+    GLOBAL_EXECUTOR.spawn(future)
+}
+
+#[cfg(feature = "unstable")]
+pub(crate) fn local<F, T>(future: F) -> async_executor::Task<T>
+where
+    F: Future<Output = T> + 'static,
+    T: 'static,
+{
+    EXECUTOR.with(|executor| executor.borrow().spawn(future))
+}
+
+pub(crate) fn run<F, T>(future: F) -> T
+where
+    F: Future<Output = T>,
+{
+    EXECUTOR.with(|executor| enter(|| GLOBAL_EXECUTOR.enter(|| executor.borrow().run(future))))
+}
+
+pub(crate) fn run_global<F, T>(future: F) -> T
+where
+    F: Future<Output = T>,
+{
+    enter(|| GLOBAL_EXECUTOR.run(future))
+}
+
+/// Enters the tokio context if the `tokio` feature is enabled.
+fn enter<T>(f: impl FnOnce() -> T) -> T {
+    #[cfg(not(feature = "tokio02"))]
+    return f();
+
+    #[cfg(feature = "tokio02")]
+    {
+        use std::cell::Cell;
+        use tokio::runtime::Runtime;
+
+        thread_local! {
+            /// The level of nested `enter` calls we are in, to ensure that the outermost always
+            /// has a runtime spawned.
+            static NESTING: Cell<usize> = Cell::new(0);
+        }
+
+        /// The global tokio runtime.
+        static RT: once_cell::sync::Lazy<Runtime> = once_cell::sync::Lazy::new(|| Runtime::new().expect("cannot initialize tokio"));
+
+        NESTING.with(|nesting| {
+            let res = if nesting.get() == 0 {
+                nesting.replace(1);
+                RT.enter(f)
+            } else {
+                nesting.replace(nesting.get() + 1);
+                f()
+            };
+            nesting.replace(nesting.get() - 1);
+            res
+        })
+    }
+}
diff --git a/src/task/join_handle.rs b/src/task/join_handle.rs
index 110b827e..9189ea57 100644
--- a/src/task/join_handle.rs
+++ b/src/task/join_handle.rs
@@ -18,7 +18,7 @@ pub struct JoinHandle<T> {
 }
 
 #[cfg(not(target_os = "unknown"))]
-type InnerHandle<T> = async_task::JoinHandle<T, ()>;
+type InnerHandle<T> = async_executor::Task<T>;
 #[cfg(target_arch = "wasm32")]
 type InnerHandle<T> = futures_channel::oneshot::Receiver<T>;
 
@@ -54,8 +54,7 @@ impl<T> JoinHandle<T> {
     #[cfg(not(target_os = "unknown"))]
     pub async fn cancel(mut self) -> Option<T> {
         let handle = self.handle.take().unwrap();
-        handle.cancel();
-        handle.await
+        handle.cancel().await
     }
 
     /// Cancel this task.
@@ -67,15 +66,19 @@ impl<T> JoinHandle<T> {
     }
 }
 
+#[cfg(not(target_os = "unknown"))]
+impl<T> Drop for JoinHandle<T> {
+    fn drop(&mut self) {
+        if let Some(handle) = self.handle.take() {
+            handle.detach();
+        }
+    }
+}
+
 impl<T> Future for JoinHandle<T> {
     type Output = T;
 
     fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-        match Pin::new(&mut self.handle.as_mut().unwrap()).poll(cx) {
-            Poll::Pending => Poll::Pending,
-            Poll::Ready(output) => {
-                Poll::Ready(output.expect("cannot await the result of a panicked task"))
-            }
-        }
+        Pin::new(&mut self.handle.as_mut().unwrap()).poll(cx)
     }
 }
diff --git a/src/task/mod.rs b/src/task/mod.rs
index ca0b92a0..b528a788 100644
--- a/src/task/mod.rs
+++ b/src/task/mod.rs
@@ -148,6 +148,8 @@ cfg_default! {
     mod block_on;
     mod builder;
     mod current;
+    #[cfg(not(target_os = "unknown"))]
+    pub(crate) mod executor;
     mod join_handle;
     mod sleep;
     #[cfg(not(target_os = "unknown"))]
diff --git a/src/task/spawn_blocking.rs b/src/task/spawn_blocking.rs
index e9ed0c5a..9c836f24 100644
--- a/src/task/spawn_blocking.rs
+++ b/src/task/spawn_blocking.rs
@@ -1,4 +1,4 @@
-use crate::task::{JoinHandle, Task};
+use crate::task::{self, JoinHandle};
 
 /// Spawns a blocking task.
 ///
@@ -35,8 +35,5 @@ where
     F: FnOnce() -> T + Send + 'static,
     T: Send + 'static,
 {
-    once_cell::sync::Lazy::force(&crate::rt::RUNTIME);
-
-    let handle = smol::Task::blocking(async move { f() }).into();
-    JoinHandle::new(handle, Task::new(None))
+    task::spawn(async move { blocking::unblock!(f()) })
 }
diff --git a/src/utils.rs b/src/utils.rs
index 31290e33..f3299f63 100644
--- a/src/utils.rs
+++ b/src/utils.rs
@@ -61,15 +61,15 @@ pub(crate) trait Context {
 
 #[cfg(all(not(target_os = "unknown"), feature = "default"))]
 mod timer {
-    pub type Timer = smol::Timer;
+    pub type Timer = async_io::Timer;
 }
 
 #[cfg(any(feature = "unstable", feature = "default"))]
 pub(crate) fn timer_after(dur: std::time::Duration) -> timer::Timer {
-    #[cfg(not(target_os = "unknown"))]
+    #[cfg(all(not(target_os = "unknown"), feature = "default"))]
     once_cell::sync::Lazy::force(&crate::rt::RUNTIME);
 
-    Timer::after(dur)
+    Timer::new(dur)
 }
 
 #[cfg(any(
@@ -84,7 +84,7 @@ mod timer {
     pub(crate) struct Timer(futures_timer::Delay);
 
     impl Timer {
-        pub(crate) fn after(dur: std::time::Duration) -> Self {
+        pub(crate) fn new(dur: std::time::Duration) -> Self {
             Timer(futures_timer::Delay::new(dur))
         }
     }