Do you ever write down things in the hope you never forget them, but still think it would be better if you could somehow take a test of that subject from time to time to make sure you don't forget?

I do, and I found it quite difficult to keep the knowledge live without having to reread the things every now and then. For that purpose, I started writing a simple JavaScript/XML/XSL fileset that allowed me to present questions (randomly if necessary) from a structured set of questions. In the beginning, it was too simple to share (string matching) but quickly grew to something more elaborate: regular expression support, multiple string-answer support, in-paragraph answer boxes and single/multiple choice answers.

With this fileset in place, I can keep track of things I would most likely otherwise forget: just select the category which I want to take a test from, and start with a (lot of) random question(s).

I've decided to put this fileset online (including demo files) and will extend the demo file with questions regarding my book, Linux Sea, allowing readers of the book to take online tests after they've finished a chapter.