With Windows UAC, when you run a program it opens a pop-up saying "do you want to run this program" and you can click "yes" to continue. With a Mac, if you run an unsigned program it opens a pop-up saying "program cannot be opened because the developer cannot be verified" and your options are "Move to Trash" or "Cancel". It doesn't mention anything about letting you open the program anyway. This means that if you want to develop software targeted at anyone who doesn't know to go to the security section in System Preferences when they're not prompted to do so, you have to pony up $100 for a developer license. A lot of open-source projects don't offer Mac builds for this reason, and you have to build from source instead.