I have historically gone with PostgreSQL and had no complaints. The licensing issues concerning MySQL also give one pause (Oracle are greedy bastards who will use any excuse to extract money from captive customers, so depending on their properties is to be avoided). Having said that, these days, SQLite is probably sufficient for many workloads and has the advantage of not requiring a database server.

And pig farms

Helping techbros loot the commons.

Have they figured out how to make access-controlled posts (i.e. friends-only, or for specific subgroups) work with ActivityPub federation, or are all your posts public and visible to anyone, as on Mastodon? If people are going to start using this platform, there will need to be an option for making posts visible only to friends (and “followers only” is not a viable alternative).