TNT has been around since about 1998. These days the TNT project lives on SourceForge; it is maintained and updated by a handful of developers that enjoy using TNT day-to-day.
The latest TNT release is 2.6, released on Mar 28, 2006. Download it here.
This version supports the TOC 2.0 protocol and has been working reliably for many months.
GNU Emacs users: TNT seems to be flaky in GNU Emacs, but reliable in XEmacs. We've yet to track this down; any ideas are welcome!
If you have code or ideas you'd like to contribute, that's great! Drop an email to the tnt-devel mailing list to introduce yourself. We're a casual, friendly group.
SourceForge provides forums and defect tracking, but those areas are pretty dead for TNT. Most of our traffic is on the tnt-devel mailing list. Feel free to ask questions there.
TNT lives at http://sourceforge.net/projects/tnt.