Eclipse Collections is a collections framework for Java. It has JDK-compatible List, Set and Map implementations with a rich API, additional types not found in the JDK like Bags, Multimaps and set of utility classes that work with any JDK compatible Collections, Arrays, Maps or Strings. The iteration protocol was inspired by the Smalltalk collection framework.
Eclipse Collections started off as an open source project on GitHub called GS Collections. GS Collections has been presented at the JVM Language Summit in 2012 and JavaOne in 2014. There are two articles (part one and part two) on InfoQ.com showing some of the capabilities of the collections framework through examples. A performance comparison between the parallel lazy implementations of Java 8, Scala and GS Collections was presented at QCon New York in 2014. A set of memory benchmarks is available here.