I have no idea how to track things. I use to write blog posts for that, but the idea of a blog post is to share knowledge with others.
At work I have a "howto" folder with random stuff, but it died as I don't take the time anymore to write things down.

I used shell scripts as documentation before, and it works great!
Unfortunately it doesn't work for ideas or concepts... I might start making "presentations" using sent(1), the suckless presentation tool, as the text format is simple amd it can include images.
Another idea would be a braindump gopherhole, which is simple as well, and can be accessed remotely.