Persistent (immutable) collection library for Java
Common utilities and classes for collections.
Efficient Java collections for primitive integer types
A supplement to the Java Collections library.
Dynamic Collections provides a suite of tools to extend and enhance the Java Collections API.
Ponzu 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.
Collections library of the Staccatissimo project, focused on providing new abstractions that mix object oriented and functional programming style for dealing with iterable objects.
Collections and utilities based on primitives types
Trove of primitive collections with Apache 2.0 license, built for Java Java 6 or 7