Open Source is the license that De Monsters are releasing De MonsterDebugger, to be more specific it is released on a GNU General Public License. De MonsterDebugger is a tool that we created to help us with debugging the applications that we build in Flash, Flex and AIR. We reckoned that we wouldn't be the only ones that could benefit from this tool and decided to share it with the rest of the world. In short the license model means that you can use De MonsterDebugger for free and can change the source code if you want to.