GDB Debugger support for MonoDevelop

Mono comes with two Mono-specific debuggers: a hard debugger and a soft 
debugger, additionally, you can use the Unix GDB debugger with Mono to 
debug low level problems.

Until the Mono Debugger is ready for production, GDB can be used to 
obtain some information about your application and debug some problems.
For more information:
http://www.mono-project.com/Debugging#Debugging_with_GDB