Unix sockets

On the other hand, varlink is a lot simpler to implement and use. All languages do JSON, most do unix sockets, some even do both in the standard library, but there are still not many languages with high-quality and maintained DBus implementations. Essentially, it's just sd-bus, glib/gio, Qt, dbus, and that's about it if I'm not mistaken.

I can call a varlink service with the Python or Demo standard libraries, or even with nc, jq, and bash, but scripting or glueing anything with DBus is still cumbersome even after all these years.

Perhaps things would be different now if we had gotten kdbus l, but as things stand today I'm more than happy to see a well specified DBus alternative emerge which seems to hit the sweet spot between simplicity for simple use cases while still allowing for incremental complexity for more complicated situations.