PunBB is the forum software I recommend most people use, and they just released a new version. They are, as far as I know, only the second system to release a table-less thread view. (The first being wp.org/bbPress.) They took a different approach than I did, and if you view the source it’s actually pretty heavy markup, but this is putting valid forums into the hands of many more people. Looks like an excellent release. Hat tip: Alex.