1. The Hitchhiker's Guide to the Galaxy, the RPG
Essentially 6 Degrees of Kevin Bacon, but for Wikipedia. Hopscotch between Wikipedia articles to find a path from say, Ashley Tisdale to HTML (Ashley Tisdale was born in California – Silicon Valley – Internet – HTML).
You can choose from a time trial, or to limit the amount of clicks you can use. Make it really hard by eliminating "the United States" as a pathway.
Play it here.
4. Geoguessr
Geoguessr is a guessing game using Google Maps. You're dropped into a random location (left) and you have to guess where you are. You can use clues (what language are the street signs in?) or you can just go with your gut. If you sign up, you can play in challenge mode against another player.
Play it here.