On Windows, a good single user database is Access. You don't need the Access database installed for your program to ue an Access database. So that's a free solution.
SQL Express is also free, but a bear to auto install and configure.
What else can you suggest that's free and easy to install?
I need to run this Silverlight Out of Browser application on a Macintosh as well. So the database needs to be easy (and free) to also install on a Macintosh.
What options do I have?