Holy carp! neo-async is fast as hell!
Crazy. Absolutely crazy. How did he do it?
It appears he removed the event emitter and some of the limit functions which was able to speed it up. Interesting.
He seems to be optimizing his versions of the async calls. I didn't look a lot through his code but you can easily see the difference. Async is only 1k lines of code his version is 5k lines.
And if you look at stuff like waterfall. https://github.com/caolan/async/blob/master/lib/async.js#L529-L560 vs https://github.com/suguru03/neo-async/blob/master/lib/async.js#L2074-L2213 clearly first one is a lot leaner while the second might run faster.