I found
Flatfort again.
Edit: Flatfort seems... buggy. Although it worked okay the first time I installed it (on my other host). I just got weirdness happening when I then moved it here. I think it was due to clicking things in a different order or something to get into the admin stuff. Or my computer is tired now and won't refresh.
Anyway, Flatfort does work, on the user end, if the back panel is a bit odd. The old version I had didn't even have an admin section, so I expect the guy is still working things out. If anyone wants to see it, it's on my site. I modified the colors, dimensions, and removed the website blank on the form so people won't sneak in porno links. Oh, just tested it, and it doesn't allow html in the message. BBcode is okay, though.
I like Flatfort because it's the only one I've found so far with a built in captcha of any kind. I don't know what I'm doing enough to mod/write/install my own captcha without help. I'm not sure how effective the six character one he's got is in the long term... but it is better than the previous one, which was only three characters and included lowercase, which made it hard to tell 1 from l or I, especially if you use Arial. I think pictures or a "Are you human?" question, or a math puzzle might be better, but then in a chatbox space is an issue, and you don't want it to be too annoying, either.