.net is and always has been free. its source code is also slightly open (meaning you can download it and use it to write your own .net framework much like portable .net and mono have, you just cant use its source code directly like other open source frameworks... not that many people have included portions of python, apache or php into their own frameworks unrelated to those products).
I still prefer to use php for web development though, which is why i think this is cool.