http://drizzle.org/
From the site:
The Drizzle project is building a database optimized for Cloud and Net applications. It is being designed for massive concurrency on modern multi-cpu/core architecture. The code is originally derived from MySQL.
The Drizzle team is removing non-essential code, refactoring the remaining code, switching to a microkernel architecture (with well-defined APIs) and generally making Drizzle into a lean, mean query-running machine.
This is sort of an answer to the NoSQL movement...