Guava is a set of core libraries that includes new collection types (such as multimap and multiset), immutable collections, a graph library, and utilities for concurrency, I/O, hashing, primitives, strings, and more!

Crunch is an alternative MongoDB driver with an emphasis on high concurrency, atomic update operations, and document integrity. It uses the Rev event library for non-blocking writes and reads. Its API is more limited than the official Mongo Ruby driver, but simpler and more Rubyish.

DispatchQueueRb is a pure ruby implementation of Grand Central Dispatch concurrency primitives. It implements serial and concurrent queues, with synchronous, asynchronous, barrier and delayed dispatch methods. All queues dispatch methods support an optional dispatch groups to synchronize on compl...

Armstrong is an Mongrel2 fronted, actor-based web development framework similar in style to sinatra. With natively-threaded interpreters (Rubinius2), Armstrong provides true concurrency and high stability, by design.

Angstrom is an Mongrel2 fronted, actor-based web development framework similar in style to sinatra. With natively-threaded interpreters (Rubinius2), Angstrom provides true concurrency and high stability, by design.

Support library to provide Futures and Promises for different concurrency models.

Mutable and immutable concurrency variable

Declarative concurrency for EventMachine

HTTP fetch client based on ruby EventMachne and EM-HTTP-Request that has configureable concurrency regardless of EM's thread pool.

Third approach to EventMachine lightweight concurrency. Runs declared methods and blocks in sequence, each in one tick. So allows calls chaining with keeping the EventMachine multiplexing facility on.

Interface for akka.io concurrency in jruby

Omnibus concurrency library for Ruby

Concurrency based polling.

Collection of utilities for managing concurrency

Massive concurrency with message-passing and stuff.

Convert video formats with custom concurrency, batch size, and conversion delay

A simple set of lightweight concurrency tools.

Provides utility classes to support common patterns in concurrent programming.

A Ruby web server designed to have a predictable and simple concurrency model, and to be capable of running in a pure-ruby environment.