It builds your C++ code with G++ or VC++'s CL.
BYP is like Google's GYP, but instead of generating your projects, it just straight up builds them using GCC or Visual Studios's CL. It's mainly targeted at C/C++/Objective-C. I was looking for a lightweight build tool that could run from the Visual Studios command line, because I don't want to start up VS just to build my code.
It's pretty minimal and built on Node.js.
BYP should be fairly pluggable at this point - you can define new build systems and add macro processors. There should probably be more work on this in the future.
You probably shouldn't use this yet unless you're willing to change stuff. (don't forget the pull request!) It's REALLY alpha. In fact, I'd be surprised if it just works in your code. It'll be more stable in a while, but I only just started it.