Not quite what you're looking for but it's fresh on my mind: 2009scape! Its an open source game engine reimplementation of RuneScape circa 2009. The devs aim for it to be purely a time capsule of RuneScape in 2009, but being open source it would be very easy to fork and add content as needed.
The official server is extremely friendly and the client has a single player mode available as well.