JRaceman uses the Mckoi Database to store all of its data.
Mckoi is a relational database licensed under GPL and written 100% in Java. It is fast, powerful, and easy to use. In fact, it is so easy to use, you probably won't even notice it: JRaceman uses Mckoi internally to manage its database so that you don't need to worry about it.
Mckoi supports both embedded mode and client/server mode, which allows JRaceman to run in single-user mode or in client/server mode, where multiple people can access the same database at once over a network.
You might notice a file called mckoidb.jar in the JRaceman distribution. This is the Mckoi database software; this file comes from the Mckoi distribution.
For more information about the Mckoi Database, including source and binary downloads and documentation, see the Mckoi Database home page.