Stumbler
Hah, this picture probably makes no sense to you. It’s a calculator with 5 buttons, but no apparent significance. Actually, these functions are the only things a computer processor can do: add numbers, memorize numbers, and compare numbers. Yet, people build everything computer-related from this foundation. It’s like the feeling you get when you think about the mathematics-physics-chemistry-biology-psychology-sociology chain.
I’m on StumbleUpon. It’s a very good example of good social networking principles: no obligation, no exit barriers, no fiery pits of infinite ignorance. I like it a lot.