Rust: What is the difference between async-std and smol?

1// async-std
2#[async_std::main]
3async fn main() {
4    async_std::task::sleep(Duration::from_secs(1)).await;
5}
6
7// smol
8fn main() {
9    smol::block_on(async {
10        smol::Timer::after(Duration::from_secs(1)).await;
11    });
12}