I would guess this one, but I don't think any usernames carried over. Except maybe the one I can't recall right now (startup related to streaming video over .gif back in late 90s iirc).
I actually know which one he is talking about, but since he didn't call it out, I won't either (maybe they like it quiet).
But what happened was that Joel freaked a bit out over some of the drama on the Business of Software forums and shuttered them, in spite of them being very popular and having a huge community - another one of those weird decisions. In an alternate timeline, they would have been HN.
Not to drag up dirt, but the drama was someone’s quite public suicide and I suspect Joel concluded the bad PR wasn’t worth the good will generated otherwise.
When Joel stopped publishing articles there wasn't any content to drive the conversation. However, it was still a pretty popular forum when it was closed by Joel.
I think it's successor peaked in popularity way after that but started to drop off as there was no obvious way to get new users. The old method of people checking their HTTP logs for referrers to see who was linking to their content and then joining the conversation stopped being a thing.
But what happened was that Joel freaked a bit out over some of the drama on the Business of Software forums and shuttered them, in spite of them being very popular and having a huge community - another one of those weird decisions. In an alternate timeline, they would have been HN.