It's a very recent fork of ownCloud, so if you know what that is, most of your knowledge transfers. It's basically self-hosted Dropbox/Google Drive/OneDrive, with some initial support for other cloud-y things: web-based document/spreadsheet/presentation software and chat/call/video conference being the main two. The value proposition is all in the self-hosted part. If you have a problem with giving a third party access to all of your files, this is a possible alternative. If you trust Google/Microsoft/Dropbox with your files, your life will probably be a whole lot easier letting their massive engineering and ops teams manage servers and software for you.

It's definitely not an all-in-one small office solution, there's no email app.