All-Knowing Mind is a Java/SWT multi-language, OS-independent game server browser focusing on first person shooters similar to Yahoo's now defunct All-Seeing Eye.
quake4j is a Java implementation of the original Quake engine. The game client can be launched from any web browser with one click, and lets you play deathmatch games with other quake4j users.
jQuake3Eye is a server browser for Quake3 Arena written in Java (sun).
It allows to monitor your favourite quake 3 servers.
With jQuake3Eye you can see the players present on a server and join the game.
Watch your favorite servers to find your buddies
Ruin is a 2.5D Java game world that can run from a browser. It's like a 3D MUD. The game looks similar to Doom or Heretic. View the home page for a demo (http://ruinworld.sourceforge.net).
Tanfrag will be an open source 3D First Person Shooter, using the JAVA programming language, and will be primarily for the Windows OS. Tanfrag will be using the WildTangent Web Driver which puts 3D DirectX capabilities into your web browser.