Currently, there are several Java Applets that provide basic ``chat'' functionality. For a list see e.g.: Java MUD Interfaces page. One drawback of those applets are that they need to be installed on the same machine as the MOO runs, so *you* can't install it on your (moo client) machine. Another drawback is that they are not very suitable for construction and development work (as of Oct/96). Get a ``real'' client like tkmoo-light or an emacs-based client if you work under Unix and know emacs.
At TECFAMOO: Check the the TECFAMOO pages, e.g. http://tecfa.unige.ch/moo/how_to.html for information on currently installed applets.