I have tried starting a few side projects that are completely different from my day job, but the scattered hours that I get to work on them makes it twice as hard to get anywhere with them.

Now my side project is based on the database I have built at work (as an in house project). It makes it so much easier, as the hard non-coding problems are usually well understood, as I have thought about them before. I can pick it up and leave it without forgetting anywhere near as much. And it gets rid of the frustration I have at work, because the quality of the code is always ignored in favor of new feature that were needed yesterday. Same thing but with nicely written code.