ScalaSTM is a lightweight software transactional memory
for Scala, inspired by the STMs in Haskell and Clojure.

ScalaSTM provides a mutable cell called a Ref. If you
build a shared data structure using immutable objects and
Ref-s, then you can access it from multiple threads or
actors. No synchronized, no deadlocks or race conditions,
and good scalability. Included are concurrent sets and
maps, and we also have an easier and safer replacement
for wait and notifyAll.