Seems there is quite a bit of confusion about "Open Source Software" (OSS) and "Free Software" (Freeware) here, and I'd like to clarify things as the two are *very* different. The key elements here are "Free" and "Freedom"
Freeware is software that is free to use. And that's about the only thing free about it. You do not have the freedom to make changes tot he software or to add new features.
Ope, Source Software is not only free to use, but you have the freedom to do anything you want with it. You have the freedom to alter it, and in many cases, you even have the freedom to sell your modified versions.
For example, while Centrafuse and Frodoplayer are free software, they are NOT open source software. RoadRunner and PyCar, onthe other hand, are a good example of open source software.
[edit: examples fixed]