InMemoryDatabase
InMemoryDatabase: "An in-memory database (aka embedded database) is a database that runs entirely in main memory, without touching a disk. It's usually created when a process starts, runs embedded within that process, and is destroyed when the process finishes.
On first blush the idea of such a beast seems ridiculous. The two main purposes of most databases are to persist information between process invocations and to handle concurrent access to data between processes. In-memory databases do neither - so what's the point?"
..once again a good article from Martin Fowler, this time about In-Memory-Databases..