Humble Bundle?

Basically, it's a bundle of games for charity.

It is pay what you want. If you pay $1 or more, you get Steam keys and DRM-Free versions. If you play less than $1, you get only DRM-Free versions. And you pay for the entire bundle

You have to pay at least 1$ to get steam keys.

It's a bundle made of games (check list on the official site). Usually. The ones which aren't are noted by HB. Yes, pretty much anything above 1$ will get you Steam key. There's also Above the Average which means that if you pay price that is above the current average you get bonuses.

At least 1$ for steam keys. Yes in general they are steam keys.

Steam keys so far as I know.

and yes, but you get extra stuff if you pay more than the average, also you decide who gets how much of what you are paying.

Its a pretty cool system overall.

Yes. But the minimum for getting Steam keys (if the game is on Steam) is 1$. There are also "BTA" (Beat the average) prices that will unlock more games.