I have something called "Diensttagebuch", which is awkward to translate ("Duty diary"?), it's a Jekyll blog (currently at https://www.pchr8.net/d/dtb/) for things I know I'll have to google later. I have two bash scripts for creating-or-opening a new page and for deploying (upload to server + commit to git). I use https://github.com/rking/ag.vim for searching though the Markdown files on my local machine.

For more general knowledge, Semantic Mediawiki (http://pchr8.net/f/), but it's basically a big link database now. I can sort it by rating / complexity / to read / domains / keywords and found it quite flexible.

Also, Anki for things I want to memorize. https://www.gwern.net/Spaced-repetition describes the theory quite well.