A fast, open source, in-process database with a TCL API.
"Berkeley DB is the leading open source developer database in the world with over 200 million deployments. Customers rely on Berkeley DB for fast, scalable, reliable and cost-effective data management for their mission-critical applications. Berkeley DB is part of Oracle's embedded database product line, which includes Oracle TimesTen for high performance in-memory database applications and Oracle Lite for mobile applications."
Sleepycat Software was acquired by Oracle Corporation in February 2006, which continues to develop and sell Berkeley DB. As of Berkeley DB release 6.0, the Oracle Corporation has relicensed Berkeley DB under the GNU AGPL v3.