Everything you work on outside of work is your own property, and we have no real interest in it. Even on work computers, as long as it's not part of a client project, then it's your property.
Honestly, I'm kind of surprised how many companies seemingly don't work like this. I mean, maybe I'm really lucky in that sense, but I never worked for or even interviewed at a company that cared what their employees were doing in their free time.