Well, we were down through the month's passing, so to make it sound more dramatic, I've written the subject that way.
What a stupid mistake. I'm sorry. I transfer all the sites - 193 sites - from the old server to the new server. Of all of those, two sites failed and I hadn't noticed because cPanel/WHM didn't show me any fatal errors. Numerous little inconsequential errors, but I checked nearly 100 sites by hand after the first batch, so I spot-checked the second batch, and hence missed that forum.simutrans.com didn't get transferred. Everything else did, except one other tiny site.
And I've been busy - I usually check the forum every day, but sometimes it's 2-3 days or so between coming here.
So I dropped the ball. I'm really sorry, guys. But the good news is that we're back and everything should be here.
Thanks to Yonatan for poking me on Facebook.
Nobody is infallible - it is a splendid thing that you host the forums at all.
Peace to you.
I seconded jamespetts.