OI Calendar-Sync let you synchronize your agenda between Android and the Web.
It is build with Blockstack and uses Your decentralized identity and storage - no account creation needed, just your Blockstack ID.

Note, that this is not a replacement for your calendar app. OI Calendar-Sync adds
your events from the Web app OI Calendar to your Android calendar app (thanks to Android's content providers).

Current limitations:
- Changes on Android are not sync'ed to the Web
- Web app is fixed to cal.openintents.org

The app is free and open source!