Piwik: As of 2017, more than 1 million websites worldwide use it, making it a clear alternative to Google Analytics. 

OpenOffice: OpenOffice offers a powerful package combining word processing, spreadsheet, and presentation software. 

Nextcloud: Nextcloud provides a remarkably well-designed way to access your files wherever you are. 

Mail-in-a-Box: Mail-in-a-Box lets you become your own email service provider without having to become an email deliverability expert in the process. 

HackMD: HackMD is a great, collaborative markdown editor that runs in the browser. That means you can work together on an idea with your colleagues, no matter where they are located. You can try it out on the hosted site, or you can host your own version.

The programming language R

WordPress