Commons Collections
Commons-Collections seek to build upon the JDK classes by providing new interfaces, implementations and utilities.

Commons Primitives
Apache Jakarta Commons Primitives provides a collection of types and utilities optimized for working with Java primitives (boolean, byte, char, double, float, int, long, short). Generally, the Commons-Primitives classes are smaller, faster and easier to work with than their purely Object based alternatives.

FastUtil
Fastutil extends the Java™ Collections Framework by providing type-specific maps, sets, lists and queues with a small memory footprint and fast access and insertion; it also includes a fast I/O API for binary and text files.

Mango
Mango is a Java library consisting of a number of iterators, algorithms and functions, loosely inspired by the C++ Standard Template Library.

PCJ
Primitive Collections for Java (PCJ) is a set of collection classes for primitive data types in Java. The goal is to provide an efficient alternative to the Java Collections Framework (JCF) when using primitive data types, such as int, boolean, or double.

tclib
Type-Specific Collections Library restores the type checking responsibility to the compiler and assures that errors are caught before they're turned into executing code. Getting rid of the casts also makes your code cleaner and easier to understand.

Trove
Trove provides a "free", fast, lightweight implementations of the java.util Collections API.