Dash is a documentation browser for developers. It contains plenty of datasets covering everything from web development to building native apps.
It's an alternative to browsing documentation using your IDE, and to Googling around - and it's a fast alternative. Your documentation is synced offline, so it will save you a few seconds with each search. Added up throughout the day, it might be quite the significant amount of time saved.
The Mac version is $24.99, but you can try it for free without any time limitation.
The iOS version was pulled from the App Store a few months ago, but as of May 25th 2017 it is again available and for free.