Idea for Paid Premium Pro Service:

Add a version history feature to Calendar and Adressbook data.

For me it is very important to preserve my Data. I live currently always in the danger to accidentally delete some of my data because of my own fault or by a software or synchronization error. If I sync my calendar across several devices using your or a similar service and delete 1 entry at the first device it gets automatically deleted at the second and vice versa.
The same goes to loosing partial data. If I edit a text field and the client software is outdated and supports only 50 characters at a headline and I had first a text of 80 placed into this field at my desktop I will lose the last 30 characters during a sync. Same goes to other similar actions. I'm unable to get this information later back because I can't compare what has changed and I know currently also no solution for this.

I would say your service could fill this gap! :-)

How to do this?

Create a web frontend to at least view the data stored at your cloud. It doesn't need to be a full functional calendar or adressbook. But it should display all fields which are contained at each dataset.

Now add a version history to this data on your server which is the big enhancement of CalDAV and CardDav and the power of this proposal. Make is possible to display changes between each sync if there were any modifications and make it possible to view deleted Items.

I hope you like my proposal and think seriously about it. I'm currently thinking about getting a Pro Account at your service only to support your Idea. Compared to the free I have currently no stimulus to upgrade. Such a "version history" feature would change this completely. And I think others would like to have more security, too.

Thanks a lot for creating a independent alterative to the big global players. Keep on the good work. :-)