I sadly work for a company that claims ownership of any kind of "technical" thing I come up with. I have dozens of side-projects that I work on, but sadly they're all kind of stuck running in my basement until I leave my current job.
I've managed to get exceptions, but for the most part, this is why I have always preferred being a 1099 contractor. They can only specify client-specific IP ownership and I get to do my own thing without legal repercussions.
Side dish = product built on a platform the customer already uses. Example: Streak (a side dish) is a CRM that lives inside Gmail (the main dish).