Collectively known as "The Front Page of the Internet" Reddit connects people from all over the world through their shared interests. There are a number of apps that have been created for both Android and iOS platforms, simply get to your favorite smartphone/tablet application provider, and search "Reddit."
Recommended Learning Sources (which also have applications available)
An application (also available in iOS) that teaches the user in simple, step-by-step instructions how to tie knots of every variety. The creator of this application has several other highly rated applications as well, including ones covering Anatomy and Wilderness Survival.