I would say windows and it's developer tools. It was the first platform that enabled engineering collaboration on such a scale that the world has never seen bef

I would say windows and it's developer tools. It was the first platform that enabled engineering collaboration on such a scale that the world has never seen before - between any hardware/software/library designer - all while making the fruits of this efforts extremely accessibly to the common people. And it succeeded in running the "mind of the world" for quite a few years. On the same note i would add the internet, but i'm torn, i think(maybe mistakenly) that windows is a bigger engineering achievement - something much harder to pull off, and the internet on the other hand is brilliant in it's conceptual simplicity{ routers + links + packets + redundancy + intelligence at the edge} - although the implementation has definitely pushed many boundaries.