Is there an open source lightweight RDBMS supporting SQL with zero management?

My application needs RDBMS support. There are not many users access it in the same time and the data stored in it is not large. MySql is good but it is not easy to manage it.

I think I can use sqlite to implement it with thin socket wrapper, but I want to know if there is an open source RDBMS just like this now? I hope it can support both linux and windows system.