The law usually says work done while you're employed belongs to the employer. Off topic: at least in my country this is a special exception to the general "auth

The law usually says work done while you're employed belongs to the employer. Off topic: at least in my country this is a special exception to the general "author" legislation, which says for example a painting you make for a buyer will forever be "by you", and even after selling it you still retain some rights. In software, what you write belongs to the company, period. Now depending on the specific wording of the law and in your employment contract you may or may not be able to work on something related on your own. The only solution I can think of which would not require a lawyer and/or reading a lot of legalese is making a piece of paper in which you grant the company the right to use your software and the company agrees it's yours, and get your boss to put the company's stamp on it. That would work in pretty much all cases I can think of, and it's reasonably easy.