From Kyle Gabler, co-developer of World of Goo:
The Human Brain Cloud: a massively Multiplayer Word Association Game!

You will be shown a word. You will type what you first think of. You will be shown another word. You will type what you first think of. Ad infinitum. But it’s fun! The idea is, the more a certain “link” is made, the “stronger” that “link” will become. No need for registration. And no cookies (in case you care)!

You may have played something similar with friends. This lasts forever! And all words are words other people have entered. You can view the graph (a few nodes at a time) at any moment, and see what other people think. It’s quite enjoyable, and certainly a nice distraction. You might get a bit bored if you go for very long stretches though.