The "during work" part is ambiguous. I read this to mean during working hours. The boss seems to be interpreting it as "while employed", so including spare ti

The "during work" part is ambiguous. I read this to mean during working hours. The boss seems to be interpreting it as "while employed", so including spare time. But you don't want to get to the point where legal action is taken to test it. If you released a competing app to your employer, I'd expect legal action. I generally refuse to sign contracts that claim ownership over any IP I create out of work (although I would accept it if the IP in question directly relates to my employment). Even if the company appears to have good will here, you need to be careful. One company I worked at went through a merger. Their lawyers tried to argue that the software I had created in my spare time now belonged to them. The original company would never have done that. Luckily I had a different contract to the standard one as I had those clauses removed :).