[rafifyalda]

Not to mention you can import and make your own DocSets, can integrate it with Xcode and much more. If you're developing anything on a Mac, you should probably have this installed (and pay to support it of course).

It's also a snippet manager, though I don't think many people use it for that purpose.

[orta]

Dash has great support for CocoaDocs too so you can import open source libraries' DocSets. ( disclaimer: I made CocoaDocs. ) for example: http://cocoadocs.org/docsets/AFNetworking/1.3.1/