Some explicitly single-user ActivityPub software to check out
Technically, anyone with the knowledge and interest can spin up a single-user ActivityPub server and go about their business, but generally these servers aren't being developed with that usage in mind. In other words, they can be overkill for individuals in terms of features or resource use.
That's where single-user software comes into play. Explicitly developed for individuals, or in some cases very small groups, to use, this software is lighter on resources and more focused in its features for individuals.
As to why you might want this: it enables you to benefit from many of the benefits of ActivityPub, connecting and engaging with others & building your own curated feeds, without some of the drawbacks of multi-user servers such as keeping up with federation/defederation decisions that may affect what you can interact with & follow.
So on to a couple lists, in no particular order:
"Microblogging" but with relaxed character limits:
Rhyming slang isn't really supposed to be funny, rather obfuscatory. It's almost like a cipher, so that anyone not in the know doesn't understand. That's a theory, anyway.