I have a "tinker" directory with decades worth of small, just-for-fun projects I've coded. Many of them are bleeding-edge browser experiments, and I don't want to bother with "requires such-and-such browser" messaging, I just want to see what is possible.

For most of them, building the thing is fun and instructive--and every once in a while I can draw from this reservoir of creativity for new public-facing projects. It's great!