Pixelfed is basically a federated alternative to Instagram that's been picking up a massive amount of momentum. The Groups feature is more or less federated Facebook Groups, with a bunch of robust tools built in, and will be compatible with Lemmy communities and Kbin magazines.

The reason this is significant is that it may prove to be the final push that makes groups a standard part of the Fediverse experience. Some of the biggest platforms in the space have lacked it, for years and years. This implementation could prove to be a really good blueprint of what the standard experience ought to provide, at a bare minimum.