* Ponylang. Pure Actor model. Static typing to enforce safe concurrent semantics in almost all respects. Plus ORCA GC. Upshot: high performance, and type theory grounded guarantees of no deadlocks, no livelocks, and no data races. Chief downsides are that MS Research has hired its founder, and it's a fledgling language/community.

* Elixir. Kinda Actor modelish. Dynamic typing, solid community. Someone else has posted about it.

* Raku. Someone else has posted about it. Chief downsides are that it's got slow single core performance and small community. Upsides include ease of use for multi core code. `start` schedules a lambda or function or statement on a virtual thread. cf Go's `go`. No `async`.

Java also has some basic thread synchronization primitives built into the language. It's way easier than you probably think. And it gets even more interesting with the upcoming project loom, which gives you the same programming model for lightweight and real threads.

Async programming is a pox on the industry. It's very useful in rare situations that require extremely high performance, but for general business processing, function coloring adds a ton of accidental complexity.

The millionth prime number using 1 CPU:

    $ raku -e 'say (1..Inf).grep(*.is-prime).skip(999999).head'
    15485863
    real 0m5.515s

    $ raku -e 'say (1..Inf).hyper(batch => 10000).grep(*.is-prime).skip(999999).head'
    15485863
    real 0m2.036s