It was asked a couple of months ago, but given the AI enshittification, it seems a good time to ask again.

I looked around and found:

• Pinetta is/was in development but seems dead with only an alpha release. I am chasing this up on Matrix. edit: Apparently still, technically, active although progress has been slow
• Pinry is a FOSS alternative, but not federated, that seems dormant. However, it works and is in Python, so someone could bolt an AP server to it, he says airily.