VimGenius
"Increase your speed and improve your muscle memory with Vim Genius, a timed flashcard-style game designed to make you faster in Vim."

Regex Crossword
"Regex Crossword is a game similar to sudoku or the traditional crossword puzzle... In Regex Crossword you are not given a word to guess, but a pattern that tells you which letters are allowed."

Coderbyte
"Solve programming challenges, write algorithms for games, participate in competitions."

Codewars
"Earn honor and ranks, customize your training, crowdsource the best solutions."

Try Foundation
An interactive playground to help users get familiar with Zurb's Foundation front-end framework. Fairly simple stuff here, but a quick way to get introduced to a well-established framework.

Git Immersion
"Git immersion is a guided tour that walks through the fundamentals of Git, inspired by the premise that to know a thing is to do it."

explainshell.com
This looks really helpful. Just enter a shell command and this will give you a plain English explanation of what each part of the command does. Nice if you're copying and pasting from somewhere and want to ensure it does what you think it does.

nodeschool.io
"Install these choose-your-own-adventure style lessons and learn how to use node.js, npm and other related tools by writing code to solve realistic problems."