I would search codeproject for examples of using Managed Extensibility Framework (MEF). I did a quick search and the latest versions should work under Mono. Try: http://www.codeproject.com/Articles/56635/Managed-Extensibility-Framework.aspx for a MEF intro. Going the MEF / roll your own solution route you can't avoid writing some OS specific code to start your "services" with the system but that shouldn't be too hard. Option 2: Check out http://linux.die.net/man/1/mono-service[^] which basically allows you to run .net windows services under mono/linux with little if any code change required.
~Justin_H