[velikos]

The fact that it's branded with Windows makes me hesitant to use it for non-Microsoft environments.

[adlpz]

https://github.com/winjs/winjs/blob/master/License.txt

It's Apache 2.0. If it's good right now, there is no reason whatsoever to not use it.

[sharpneli]

Unfortunately it isn't good right now. It's pretty much IE only in practice. It might become good eventually but it's not there yet.