A fast, open source, in-process database with a TCL API.
From http://www.sleepycat.com/index.html
"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."
http://www.sleepycat.com/docs/api_tcl/api_tcl.html