Create a Calibre (eBook) server

Calibre is an eBook organiser and library server/app. It allows sync to mobile eReader devices, conversion between formats and reading of your library online. It is open source, cross platform and can install with a GUI. It can successfully be run headless in a server-client operation (according to my research). I'm not 100% sure, but I think a standalone GUI version can be set to sync with a remote server version too if you so desire (although IMO it would be better to use in client-server mode).