Best (self hosted?) blogging/wiki platform?

[Guyren Howe]

I have my own website on my own server, currently covered in digital cobwebs.

I’d like to replace it with a good blogging/wiki platform. Ideally using Ruby,  but that’s not required. Ideally using Postgres but again, not required.

Open source. Multiple domains/sites/users. Ideally with a good beginner-friendly mode, so I can share it with friends.