ownCloud is a free and opensource file sync and share app which is self hosted.

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

fruux is a cross-platform synchronization service.

Floola is a freeware application to efficiently manage your iPod or your Motorola mobile phone (any model supporting iTunes except iPhone, iPod touch).

QOwnNotes is a free open source (GPL) plain-text notepad with markdown support and todo list manager for GNU/Linux, MacOS and Windows, that (optionally) works…