Depends on your employee agreement, and where you live. Most of the companies I've worked at said that anything related to any of their business was theirs, reg

Depends on your employee agreement, and where you live. Most of the companies I've worked at said that anything related to any of their business was theirs, regardless of the times that I worked on it. Since a large company does a lot of things, you're pretty much down to selling fruit or watercolor paintings of stuffed animals, if that. (I believe that Microsoft has a blanket "No moonlighting" that they want to apply to all jobs; makes those paying hobbies interesting). My current employer doesn't care at all, and gives explicit permission in the employee contract. I can even write stuff that is in their business space, as long as I do it on my own time and equipment. Very enlightened.