It's been a long time since I last posted here, almost three months. Though don't worry, I haven't been slacking off, I've been busy working on my new project:
So what is EteSync? As it says on the website, it's a solution for secure, end-to-end encrypted and journaled personal information synchronization. It currently supports contacts and calendars on Android, and there's already a Python API, which is being used to add EteSync support to vdirsyncer. This means it will soon be available on the desktop too. I also plan on implementing tasks (to-do list), bookmarks and other personal information sync solutions, making more of our data private and journaled.
This means only you are able to access your data, your data is safe, and you can access to your data's full change history. You accidentally deleted a calendar event with important information a month ago? No problem, you can just look the event up in your change history and restore it. You have a contact and you don't know who it may be, get some context from checking the date it was created.
If you would like to see some screenshots, please take a look at the user guide, though EteSync runs in the background and seamlessly integrates with the Android system, so you won't be seeing its UI very often, you would just be using the same contacts and calendar apps you've been using all along.
Client, server and API bindings are all open source, with the source code available here. I wouldn't trust closed source solutions when it comes to security, privacy and personal information, and I don't expect you to either.