RSS / Atom
RSS and Atom have been around for a while already. Both formats are old, but not old-fashioned! These standardized, computer-readable web feed formats allow for syndication on the web, feeding materials from one place to the other.
You can subscribe to a RSS or Atom feed through a feed reader. A few suggestions:
Or have a look in the features/extentions of your favorite email client and browser!
More suggestions for feed readers can be found here.
You can also subscribe to the ActivityPub feed through one of the Fediverse projects.
The Fediverse is a federated network of different software projects, instances and communities, that can operate on their self-determined conditions and yet communicate with each other.
The ActivityPub feed will be posted from the https://social.servus.at Mastodon instance, but can be followed from any other instance on the Fediverse. A few suggestions:
More Mastodon instances can be found here: https://joinmastodon.org/.
Or if you want to dive deeper into the Fediverse, this is a good place to start: https://fediverse.party/.
And diving into the ActivityPub protocol can be conveniently done via here: http://www.activitypub.rocks/.