I don't think any forum system has custom thread fields by default, although it makes a lot of sense IMO.  Stuff like post icons seem redundant when you have custom fields.

The thread you posted does show that GARS is a similar system, but for vBulletin: http://www.thevbgeek.com/geekmart.php?do...http://www.thevbgeek.com/geekmart.php?do=displaypr
Not free, so can't check it out (could try obtaining it through other means, but really can't be bothered), but it seems to be more targeted at being easy to use rather than being as powerful as XThreads.

Surprising that there really isn't even plugins of similar nature for other forums, then again, I came up with the concept of XThreads myself (only just recently discovered GARS).