Common utilities such as MultiIndexMap (an efficient implementation Map, V>), ConcurrentMemoizer (simplifies and wraps the lazy construction and memoization of expensive operations), StreamUtils, MapUtils, SetUtils, etc. which - among other common static convenience methods - use LinkedHashMap/Set, rather than the default HashMap/Set that the base Java statics in Stream, Collectors, Map and Set, and much other commonly sought-after functionality such as Validation (which holds common many parameter checks), AtomicDouble, IStreamable, and IPartitionable