HexOS is a fully capable server OS on the back end, with all the difficult technical knowledge requirements that entails. The difference is that the front end is smoothed and curated for ease of use by those of us that aren't willing to devote weeks and months of our lives
Its main focus is as a file storage server, but it can also host many interesting things such as local media servers (build your own netflix, spotify, etc), or game servers (minecraft, etc, etc), Voice communication servers like Teamspeak... the list goes on.
Basically, its a platform to host and back up your files, AND host other apps if you want to.