Garage : An open-source distributed storage service you can self-host to fullfill many needs.
CryptPad : CryptPad is the Zero Knowledge realtime collaborative editor.
Encryption carried out in your web browser protects the data from the server, the cloud ...
Kinto : Kinto is a lightweight JSON storage service with synchronisation and sharing abilities.
Gerrit : Web based code review and project management for Git based projects.
Zulip : Powerful slack-like open source group chat
droppy is a self-hosted file storage server with a web interface and capabilites to edit files and view media directly in the browser. It is particularly well-suited to be run on low-end hardware like the Raspberry Pi.