I've noticed it mainly through CloudFoundry but just not too sure what its supposed to be doing. However I am guessing its probably something pretty big as why else would VMWare be supporting it?
Solution
It's an...
Efficient and 100% event driven IO framework,
flexible enough to use the best underlying OS features it can find,
presenting an API in a high-level programming language (the same language your client-side will most-likely use),
implemented on top of the best available intepreting engine for that language, and
supporting more and more third party libraries with each passing day.
Effecient in server side api, avoid using for CPU intensive operation