fruux is a unified contacts/calendaring system that works across platforms and devices. We are behind sabre/dav, which is the most popular open source implementation of the CardDAV and CalDAV standards. Besides us, developers and companies around the globe use our sabre/dav technology to deliver sync functionality to millions of users.
We were super frustrated with the state of address book and calendar sync. We wanted to build a system that’s reliable, easy to setup and use and has a great interface. We started with synchronization of personal data, but progressed over sharing functionality towards team and enterprise features.
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If you've not tried fruux yet, then why not check us out and let us know what you think! And if you're already using fruux, then we'd love to hear your thoughts and comments. You can also suggest a feature for any upcoming releases or tweet us: @fruux.