Primitive-type collections based on CERN's Colt Java API
Eclipse Collections API
GS Collections is a collections framework for Java. It has JDK-compatible List, Set and Map implementations with a rich API 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.
Persistent collections based on 2-3 finger trees.
OPS4J Base - Utilities/Extensions related to java collections.
Jcommon Collections Package
Efficient collections for sets and maps that has primitive types as keys.
Utility library for collections, comparators and iterator classes
This library provides efficient implementations for various collection data structures (esp. linked lists and priority queues), which have very insufficient implementation in the Java Collections Foundations that makes it hard or even impossible to exploit their efficiencies.