Solarpunk

You can modify it to do what you want more or less. The only common core is that it is all federated via ActivtyPub, the rest is decided by modules, which include microblogging like Mastodon, but I think (not entirely sure) also group forums like Lemmy. It's early days for the project still.

Based on this demo the thing itself looks like a discussion forum. But that might be just one facet of its multifaceted everythingness. The documentation seems almost entirely about philosophy, intentions, aspirations, and being extendable, customizable, adjustable, adaptable, and groovy in every conceivable way. It does sound super cool, but honestly it's very hard to find the substance.