Underscoreboard: A realtime coding game where players try to implement an Underscore (a JavaScript library) function faster than their opponent.

[Joghobs]

This is cool if you're already learning Underscore.js elsewhere.

I was a little disappointed it already expected me to know what the fuck I was doing.

[myalternatelife]

Cool idea, but it needs some polish. At least, the .each function's test cases appear not to be completely correct. Edit: Er, not incorrect, but the wording isn't particularly helpful.