ONLYOFFICE™ – Cloud Office Applications for Collaboration

ONLYOFFICE™ is a multifunctional office suite that enables you to store and co-edit documents, manage projects, email correspondence and customer relations in one place.

Source: ONLYOFFICE™ – Cloud Office Applications

This is intriguing. Looks like some sort of Google Docs / MSFT Office 360 clone in open source. Uses mono to run on Linux. If it works it might be rather useful.