As far as I can tell they copied the major features and concept of Three.js, added a few extra features, but implemented it in such a way that it is only performant in a specific version of Internet Explorer. In other words, embrace, extend, extinguish.

I don't understand why people keep falling for this crap. Microsoft will do the best that it possibly can to disrupt WebGL with compatibility and other issues, just as it has always done with every key aspect of web technology. This li brary is the latest example. They could have easily made improvements to Three.js or some other existing library that was tested on other browsers but they did not. There are too many billions of dollars on the line. 3d gaming in the browser means the end of the Windows PC monopoly and Microsoft knows that whether the rest of you do or not. No I'm not exaggerating.