Types that extend and augment the Java Collections Framework.
The Apache Commons Collections package contains types that extend and augment the Java Collections Framework.
Google Collections Library is a suite of new collections and collection-related goodness for Java 5.0
fastutil extends the Java Collections Framework by providing type-specific maps, sets, lists and priority queues with a small memory footprint and fast access and insertion; provides also big (64-bit) arrays, sets and lists, and fast, practical I/O classes for binary and text files.
The Trove library provides high speed regular and primitive collections for Java.
A high performance version of java.util.LinkedHashMap for use as a software cache.
Google Collections with OSGi manifest entries
Highly Scalable Java
High Performance Primitive Collections. Fundamental data structures (maps, sets, lists, stacks, queues) generated for combinations of object and primitive types to conserve JVM memory and speed up execution.