The most up-to-date code available is probably Jonny’s final release. You can find it at https://github.com/Timtech/UniverseServer
As for public servers, only one is up right now (Jonny’s server, http://lu.jonnyvps.de/) and it’s probably the best that there’s ever been as far as public servers go. You should be able to connect pretty easily after you register on the site and read the instructions in his forum.
I don’t recommend you host the server locally, unless you want to test 0.5.1 or you know enough to use the code I linked above.