Matrix is federated and pretty good. It’s not ActivityPub though…

Basically it allows you to buy or rent your own physical servers and then use the free and open source software Ceph to setup your own cloud storage on top of them.

Depending on the scale you need, it's much cheaper than cloud storage providers, but obviously comes with the caveat that you need to manage everything yourself.

@[email protected] The privacy friendly (and cheap) option is DIY with Ceph. Managing 100s of petabytes across multiple clusters with it and it's (mostly) smooth sailing.