One of the oldest forum software still being updated and worked on is UBB.Threads. They just released version 8.0 a few weeks ago. Took them almost four years to release this update, but as far as I'm aware there's really only one true dev that works on the software still with a few helping him out since they've been using the software for years. Here's the thread announcing the update and all the features added to the software if you're curious. I've renewed my UBB.Threads license to try out the new version.
https://www.ubbcentral.com/forums/ubbthreads.php/topics/266192
https://www.ubbcentral.com/forums/ubbthreads.php/topics/266192
