The idea of all wikis being connected in a low-tech federation. An interwiki link connects one wiki to another, treating them as parts of a whole.
I contribute/contributed to the following wikis:
List of wikis I find interesting.
Two older-style wikis, which use the wiki format to add comments to pages.
List of other personal wikis I've come across. Unfortunately very software-centric.
Most web hosts will have an automated way to install a bunch of different wiki software. There are also places called wiki farms that specialise in maintaining wikis. They take care of installation and updates and tend to have useful extensions installed; leaving you in charge of you in charge of personalisation, content, and moderation.
See also: Comparison of wiki hosting services
I tend to write my notes in Markdown (may just switch to Org at some point?), so being able to easily convert from that syntax to something I can plonk into a wiki is very useful! You can even grab HTML files and stuff straight from the WWW.
☞ I don't like Markdown enough to actually use it as the markup language for the wiki, though.
MD to Doku
pandoc [inputfile.md] -f markdown -t dokuwiki -o [outputfile]
Fandom/Wikia wiki's are a pain to navigate, and I can barely open them on my phone there're so many ads. and shit.