I'm making interactive displays for public buildings like museums, railway stations, libraries, hotels, that sort of stuff. Things that let you browse thousands of high-res images and videos, or 3D maps people can navigate with information about various locations overlayed. This is all stuff that has to feel completely natural to interact with, which means it has to be extremely responsive, has to know where the person who is interacting with an element is physically standing, that sort of thing.
So that's what we're doing on .NET, and why we're using .NET. As for changing the world, my main motivation for working is being able to provide for my family, but working on something that makes you feel good is more important than I would've admitted six or seven years ago. The main reason I quit my last job was that I just couldn't work on yet another grey corporate form that would be met with the usual response of "Well that makes stuff easier for sure, but it would be better if...". I'm not under the illusion that I'm changing the world with the things I'm working on now, but seeing people use them with genuine joy and amazement is what makes it fulfilling for me.
So what are you working on that's changing the world, Bass?