If you've followed the discussions about the SMF forum software which we use here on donationcoder, you know that (despite some strong complaints from me about how they have dealt with mod coders which led me to remove my mods from their site), i think it's a really terrific piece of software and a great achievement.
They recently posted an interested interview which discusses some of the historical underpinnings of the Simple Machines Forum software:
The start to SMF was almost by accident really. We were starting code work on YaBB SE 2 but were fighting with other issues that were not code related at the time so we weren't progressing as much as we had hoped right away. One of the newer developers on the team named [Unknown] had been working on cleaning up YaBB SE and making some big changes in what he coined his "Secret Project". We had known YaBB SE needed some optimization as ultimately it was the same older functions used since the port to PHP and they drastically needed updating. When we saw what [Unknown] had in place, we scrapped what we had started and the "Secret Project" became SMF. One of the first things we did was decide on a name and a process of making the switch from YaBB SE to SMF.
During the development of YaBB SE 2 (usually referred to YSE2) we had a lot of mixed opinions on direction for the project as a whole, and on the software version itself. We had also just made it though a tumultuous encounter with a competitor that had been trying to steal our code, so the entire team was a little uncertain about which route to go.