Version 1.5 of Bitsy is out!
Bitsy is a small, fast, embeddable, durable in-memory graph database that implements the Blueprints API.
Slides: Improvements in Bitsy 1.5 by Sridhar Ramachandran.
The current production version is Bitsy 1.2 and Bitsy 1.5 is for research, evaluation and development. Webpage reports that Bitsy 1.5 should be available for production by the end of 2013.
Enjoy!