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.
I never understood pinterest. I think a different interface for https://mastodon.art should get you most of the way there. Maybe @curator@mastodon.art has a suggestion.
Yes, there may be existing options - PieFed has an image view and I suspect the *key forks could be made to do something similar.