Bitsy is a small, fast, embeddable, durable in-memory graph database that implements the Blueprints API. It is an ACID database that recovers cleanly from power failures and crashes. Designed for multi-threaded OLTP applications, Bitsy implements optimistic concurrency control and stores data in human-readable JSON-encoded text files. Common management tasks such as online backups can be done over JMX. The speed and simplicity of Bitsy relies on three design principles: No Seek, No Socket, NoSQL.
Vedis is an embeddable datastore C library built with over 70 commands. It is similar in concept to Redis, but without the networking layer, since Vedis run in the same process of the host application. Unlike most other datastores (e.g. memcache, Redis), Vedis does not have a separate server process. It reads and writes directly to ordinary disk files. A complete database with multiple collections is contained in a single disk file. The database file format is cross-platform; you can freely copy a database between 32-bit and 64-bit systems or between big-endian and little-endian architectures.
nf1db is an in memory database engine with SQL and JDBC interfaces. It supports transactions, commands from the SQL-2003 standard, all major data types, a number of functions, default and null values, auto-increments, constraints, primary and foreign keys, set operations, implicit and explicit joins, nested SELECT statements, quantity limits in SELECT statements, and much more.