aniDB
aniDB is an anime and Chinese/Korean animation database with a forum attached and some list tracking features. However, the interface and UI design is not just outdated…it’s straight-up bad. To the point that I (for example) find it more comfortable to use aniDB thru Shoko which is also pretty bad, but it’s much easier to understand.
The dataset though is pretty damn solid, though it’s been getting a little sloppy for newer stuff. There’s obviously a small and loyal userbase, but the height of aniDB’s popularity is obviously over. I think it could only recover with a pretty serious redesign that keeps all the features still in-tact.
In my “Kitsu but a front-end for Twitter” idea, I think aniDB would make the most sense for the simple fact the data is much more extensive and it could really do with a better front-end.