wargames, puzzles, and collaboration

I've been hooked on the Chess With Friends app lately. I've also been thinking a lot about turn-based games and other ways that people can play games with each other/solve puzzles together online. The first is fairly common, the latter a bit more tricky. Turn-based is a simple way to approach things, but as Chess With Friends and Scrabulous (which, by the way - Hasbro has recently dropped the lawsuit against) have taught me, some games are naturally more inclined to catch on than others. Look at it like this: with Scrabble you're pretty much only contributing to the existing board by adding a few pieces on a turn-by-turn basis. Each turn, it's you vs the board; your challenge is to add the biggest word you can that turn. You can play a handful of games against several people, and over an extended period of time. In chess, you're developing strategies and looking ahead 3-4 moves, your decisions each turn are much more connected to the development of the entire game over time. I can see extended-turn-based Monopoly, but not extended-turn-based wargames.

The real question I've been digging at lately is one of how people can solve puzzles together online. The first step is asking something of the nature, "how do people use social media together"? To this end, I've found a lot of great examples, and would like to share them sometime in the near future. Think of games you've enjoyed or services that were well put together. I've been trying to nail down the key ideas behind these things. I keep wanting to use the word "collaboration," but I think at this point we've lost a bit of what that really means, having tied it so closely to things like Google Docs and the like.

What are some of the most simple web apps/games you've found really useful? Any favorite games? How do you solve puzzles with others online?