JKhub.net and massassi.net are the best that are still updated semi-regularly.
Multiplayer should work, all you need to do is make sure that somebody is hosting a game, and that the players you want to join have your IP address. That, or else you need to all be on the same LAN together to play.
JKEnhanced can be easily installed by using this Noob friendly package
There is an "upgrade" for MotS, but it is in very early stages and so is not nearly as "complete" a change as the one for JK. You can find it here.
Find another one here
looks promising, but not no downloads yet!