Lightning App Builder is a point-and-click tool that makes it easy to create custom pages for Salesforce1 and Lightning Experience.

Kolab is a free and open source groupware suite.

Baïkal is a Cal and CardDAV server, based on sabre/dav, that includes an administrative interface for easy management.

Memotoo sync all your contacts from Gmail, Facebook, phone, Thunderbird, Outlook, etc in a single address book.

OwnDrive is easy to use free online storage service for businesses, professionals, and individuals to store, backup, collaborate and share files with others.

SOGo (Scalable OpenGroupware.org) is an open source collaborative software (groupware) server with a focus on simplicity and scalability.

Kopano is an open-source groupware application suite originally based on Zarafa.