New, simple server for live playing, using a java applet. It supports board sizes 4 to 10. No registration is necessary (nor possible, yet). Finished games are available.
Sensei's Library is a collaborative web site about and around the game of Go, but it gives excellent and up to date information about Havannah, its rules, where to play and the state of affairs concerning attempts to program the game.
This server offers a program against which you can play via the applet if you connect to port number 1964, 1965, 1966 ... (where the last digit gives the board size).