st3 looks to be a fairly promising public crate for implementing tokio's !Send local worker queues which eliminate most of the atomic operations when popping from the local queue.

Right now async_executor uses concurrent_queue for these purposes, but realistically only the workstealing operations need to be threadsafe, the local worker popping from the queue does not actually need to be Send.

Some additional scrutiny on it's thread safety model and some API compatibility additions are definitely needed (see asynchronics/st3#2).