Top 6 Scala Concurrency Projects

Akka

13 12,594 9.7 Scala

Build highly concurrent, distributed, and resilient message-driven applications on the JVM

Project mention: Carl Hewitt has died [pdf] | news.ycombinator.com | 2023-01-06
ZIO

23 3,694 9.8 Scala

ZIO — A type-safe, composable library for async and concurrent programming in Scala

Project mention: 40x Faster! We rewrote our project with Rust! | reddit.com/r/rust | 2023-01-30

The one advantage Rust has over Scala is that it detects data races at compile time, and that's a big time saver if you use low level thread synchronization. However, if you write pure FP code with ZIO or Cats Effect that's basically a non-issue anyway.
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Scala Async

2 1,135 7.1 Scala

An asynchronous programming facility for Scala

Project mention: Scala Multiplatform. Across the Universe | reddit.com/r/scala | 2022-06-18

Who said FP was mandatory? Scala is not Haskell, nor Lisp! If you don't like effect systems and all, don't use them. The choice is yours, actually. Kotlin's coroutines aren't better than what Scala offers. You can even use async/await in Scala. IMO, if you get yourself in a "callback hell" with Scala, then you're not using it properly. For comprehensions are easy to understand, and work with Futures, for instance.
incubator-pekko

1 289 9.6 Scala

Build highly concurrent, distributed, and resilient message-driven applications using Java/Scala

Project mention: Stop Building on Corporate-Controlled Languages | news.ycombinator.com | 2023-01-18

- In 2022, Lightbend changed the Akka licence, made it proprietary and very expensive at large scale
Software that starts out as more "pure", non-corporate open-source can still turn the tables on you and charge large licensing fees later. But at least if it's open source from the start, it can be forked, e.g. for Akka, there's this Apache fork that was started after Akka changed its licence: https://github.com/apache/incubator-pekko . This is the key open source protection, and it's true for both corporate and non-corporate projects.
zio-saga

1 229 5.3 Scala

Purely Functional Transaction Management In Scala With ZIO

Project mention: I want to move to Scala 3, but I'm not sure what libraries to use | reddit.com/r/scala | 2022-08-31
libretto

1 151 9.2 Scala

Declarative concurrency and stream processing library for Scala

Project mention: New Scala 3 Codebases | reddit.com/r/scala | 2022-02-17

NOTE: The open source projects on this list are ordered by number of github stars. The number of mentions indicates repo mentiontions in the last 12 Months or since we started tracking (Dec 2020). The latest post mention was on 2023-01-30.