About Matrix Matrix is an open protocol for decentralised, secure communications.
Matrix Manifesto We believe:
People should have full control over their own communication. People should not be locked into centralised communication silos, but instead be free to pick who they choose to host their communication without limiting who they can reach. The ability to converse securely and privately is a basic human right. Communication should be available to everyone as a free and open, unencumbered, standard and global network.
Fediverse isn’t explicitly activitypub only, ostatus is often considered part of the fediverse
I do agree with you. It’s a universe of federated software and matrix is federated. ActivityPub is an implementation of an idea.