As an aside, some folks may ask "why write a new app instead of contributing to Calibre Web or a similar project?" It's a good question! Because I wanted to :) Right now, this is a hobby project — I'm more interested in having fun building (rough!!) software than worried about extending existing projects. Plus, with how Citadel is designed to be backwards compatible with Calibre, you can continue to use Calibre Web.…
If there was a solid competitor that was more open, more modern, and designed with the hosted library solution in mind, I would no doubt start using it.