TwinDB is an embedded key/value database based on BerkeleyDB. It basically adds security from database corruption on top of the non-transactional version of BerkeleyDB. It accomplishes this by maintaining twin BerkeleyDB databases and using "lock" files to indicate when a set of writes are in progress. Performance is still good (tested at ~60K writes/sec and 300K reads/sec). It was written because the transactional version of BerkeleyDB is expensive.
PicoStorage, a lightweight "filesystem in a file" (structured storage) library, features efficient and compact storage of both tiny and large files and directories, compression, and transactions. It is highly scalable (and can handle directories with millions of entries), simple, and very easy to use.
ConceptBase is a multi-user meta-database system based on a deductive object manager. It is mainly intended for conceptual modeling and coordination in design environments. The system implements O-Telos, a dialect of Telos that amalgamates properties of deductive and object-oriented languages.
SQLGotcha is a tool, written in PL/SQL, to help you find sessions in an Oracle database that you want to trace. Just enter the username, machine, program, Unix PID, or even a table that is accessed. You can use SQLGotcha for both standard and event 10046 tracing, and you can make use of a unique 'waiting' mode.
Redstone Prevalent Storage is minimalistic prevalent storage for Java SE 5.0 that replaces the need for JDBC and an RDBMS for small and mid-sized applications. The library is comprised of an intentionally small set of concise interfaces and classes, and can be suitable for many types of applications where the data storage does not necessarily require an RDBMS. The library is heavily influenced by Prevayler and the Prevayler team (who should receive all credit).