Functional extension of google collections
Trove of primitive collections with Apache 2.0 license, built for Java Java 8
Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more.
jin collections is a tool libraries that help working with standard Java Collections utility in a "Code by Intenction" way. It is inspired from Smalltalk Collections Utility.
Custom Collection Implementations