The full InfinityDB 4 trial edition, most recent version.
InfinityDB is a Java embedded DBMS with a unique extremely flexible and simple API based on an ‘ItemSpace’, along with a wrapper to make the model accessible as a Java ConcurrentNavigableMap. It has optimistic transactions, data compression, multi-core concurrency, rugged I/O without a log, instant restart, a single-file data store, easy backwards data structure compatibility without upgrade scripts, and trivial management. Developer productivity is almost instant, yet it is full-featured with many utilities and example code.
After the trial period ends, an Exception is thrown on initialization.