Keeping side projects small enough to finish

My side projects get much bigger if I plan them away from the keyboard. By the time I've imagined every feature, the small thing I wanted to make has become an obligation.

I'm trying to define a first version that fits into the time I actually have. That means deciding what someone should be able to do with it, and stopping once that works. The extra ideas can stay on a list. Finishing the first version gives me a chance to use it before deciding what it needs next.