EDIT: You don’t have to answer for my specific purposes, if you use a database for any purpose yourself then please share and tell what and why.
I’m not planning to host any fediverse or mastodon instances just yet, but maybe a private email server and porting a discord channel to matrix might be in my future.
What do you use and why? Is it limited to a specific OS, and if you were on a different OS then what would you be using instead? Do you think server hardware is required for most operability or can a good desktop computer and internet speed suffice as long as downtime isn’t a problem?
Seeing your other comments on this post, I urge you to think twice about embarking on whatever it is you’re about to attempt, because it is clear you have no idea what’s in store for you. I really don’t mean it as a demeaning thing, what you’re describing is hard.
I suggest looking into a postgres tutorial first and foremost, it will teach you the basics of DBMS and how to use SQL, and when you understand that and what the database does for the applications you’re used to, revisit this project. Being a database administrator is a literal full time job in the enterprise world, and for good reason, and you don’t sound like you know enough about it to go in guns blazing.
No worries I’m not the person to jump in head first, clearly.