Pangora is a decentralized forum and link aggregator that is completely free and open, and not controlled by any company. Different sites that use pangora are each hosted by different people but users on one site are still capable of seeing content on other pangora sites (as well as other sites on the activitypub protocol such as Lemmy, Kbin, and Mastodon).
Pangora is open source with the main repositories under a copyleft AGPL-3.0 license. You can find all of the related repositories here