Today I read an article I found in www.ibphoenix.com news in entry "05-Oct-2005 Miguel de Icaza's web log provides a set by step description of setting up classic Firebird on Linux for use as an embedded database with Mono.", then I followed the link and seemed to me very interesting. You can link to the Miguel de Icaza's web log by clicking here. There you can notice how to use the embedded Firebird SQL server to use inside the Mono project (.NET for Linux). More links are there for you to follow.
By the way, Firebird is to me the best Open Source SQL server as it is very simple to administer and use, and it supports the full ACID database model. Other competitor like MySQL is about releasing this functionality. In my opinion, Firebird has very solid enterprise features.