Then someone says "Open Source Software" they usually mean software that has been released under one of the popular open source agreements. There are many advantages to this. One of the main ones being that if code was a car, the truck is no longer welded shut. Open code is there for the tinkering. Which means people all over the globe are free to tweak, evolve and improve it. If the wisdom of the crowds and the network effect kicks in and a community evolves around a particular software solution, the software can grow at enormous speed. Its like standing on the shoulders of midgets as each member in the community contributes as best they can.