Nerimity is made by Superkitten, the current solo dev in the project, with quite a few different contributors. I happened to be friends with one of the contributors, so I get it. It is self-hostable to a point (as one of my former acquaintances had tried), though there was some drama over the improper implementation. It is Electron based for the desktop app, and since I have the AppImage, it's Electron shenanigans (TS, JS and others accepted by Electron).