_.m
Kevin Malakoff (via Hacker News):
_.m is a port of Underscore.js to Objective-C. It strives to provide the fullest feature set possible in a way that is familiar to JavaScript developers (despite the differences between JavaScript and Objective-C).
There are some neat features and ideas here, but it would be interesting to see how they could be expressed with more Objective-C-style naming and syntax. I think most of the utility is in the functionality, not the low character count.
See also: Underscore.m (via Groxx).
Update (2012-08-12): Clark Goble mentions Underscore.ObjC.