Zinc allows you to play text adventure games either on your own or cooperatively over a network. It comes with interpreters for two of the most popular game formats i.e. Z-machine and TADS games, and it has a powerful map facility.
Pretty nice. The only software I know of that allows cooperative multiplayer on Z-machine and TADS games. Of course, I'm still using Java 5, and I've heard that netplay doesn't work well with Java 6.