Satsuma is an easy-to-use and flexible graph library for .NET. It implements all the necessary graph structures and the fastest possible graph algorithms.
TommyDS is a C library of hashtables and tries designed for high performance. It's faster than other similar libraries like rbtree, khash, goodledensehash, uthash, judy, nedtrie, and others.
A minimal BASIC compiler.
Functional language style immutable collections for Java.