You should write your utility in whatever is easiest for you. If you plan on selling it, sure, you might want to support as many people as possible. If it's EASY to support both OSs, sure, do it. But when you provide something to the community for free, it's completely up to you. Heck, make it run only on Unix if you want. :) As far as cross-platform languages and the engines which compile/run them, most people here don't enjoy going through the effort of getting them running. Then again, I could be wrong... :) Tony