Well, not sure about the exact date but the first posts I can find are from May 7th, 2013…
Some of us old timers will remember the somewhat stubborn transition from the clubby newsgroup format with a very small group of users - where only 25 people accounted for almost 60% of the posts - to Discourse.
(There was a previous attempt from 2012 on to transition to a web-based ‘social network’ format - based on Microsoft Ning IIRC, the format of which looked a little bit like the ‘news’ page does today - but that was not well received. The Grasshopper pages also were based on Ning, and that however was quite popular and persisted long after the general Rhino forum had switched to Discourse.)
Choosing the Discourse format, which was still more or less in Beta and whose ‘flat’ unthreaded topics, linear timeline format was completely different from the other popular forum formats was also much debated at the time.
In the end, that choice turned out to be brilliant, heralding a new era in how the Rhino community would develop and prosper. It’s impossible for me to describe how incredibly amazing this community has become - I made several attempts, then gave up - so I will just say this: WOW.
Thanks to all who have made and continue to make this forum the best place to be anywhere on the internet.