A primary goal for the project is space-efficiency. It accomplishes this by defining the five different kinds of nodes in a critbit tree - no nodes have unused or unnecessary references, and leaf nodes are collapsed into their parents when possible.
An immutable/functional implementation is provided for use where such traits are desirable. A mutable implementation with much higher insertion throughput and lower garbage collection tolls is also available.
Special thanks to rkapsi's patricia-trie project for a nice set of key analyzers and tests. If you're more concerned with Java Map interface compatibility and/or performance, you should probably use that project instead.