Main features:

• Complete class hierarchy (vs. standard JCF): Collection < ( List, Dictionary, PriorityQueue ).
• Separation of mutable and immutable collections, as in COCOA: X & MutableX.
• Reference implementations based on JCF: StaticList (arrays), DynamicList (ArrayList), DynamicDictionary (HashMap) & DynamicPriorityQueue (PriorityQueue).
• Ancillary ADTs: Queue, Stack, Relation, Sequence, Graph...
• Design patterns: Visitor, Iterator...