I wrote a review of DecSync on March 30. DecSync allows for syncing contacts, calendars, tasks, and even RSS feeds across devices without a server. While one could use a server, I use Syncthing. At the moment, I am using it to keep contacts, calendars, and tasks in sync between my computers, phones, and tablets. Using DecSync for contacts, calendars, and tasks on Android requires only an app, but the set-up is a little bit more complicated on Linux. On Linux, you have to run a local Radicale server supported by several DecSync libraries. The official installation method uses the pip package manager. I had been using the Arch User Repository package for Radicale-Decsync and its dependencies. Today, when I started the server, I ran into an error. After trying different AUR packages, I uninstalled the AUR packages I had for libdecsync, python-libdecsync, and python-radicale-libdecsync and replaced them with radicale_storage_decsync from (pip3 install radicale_storage_decsync). After installing the PyPi version of the package and its dependencies, I could again start my local radicale server with no issue and access my contacts, calendars, and tasks from Thunderbird.
Takeaway: If you are on an Arch-based Linux distribution and interested in trying DecSync for contacts, tasks, and calendars, I recommend installing Radicale-DecSync from PyPi instead of AUR if you are having issues with the AUR package (however, if you have the knowledge to modify the AUR package build, you probably do not need this tip).