For those of you wondering, I personally HAVE played the game. Its interesting in its own right, and personally I didn't find it much fun, but there is appeal in playing games AND having a real impact on the world. Plus, if you do help during a break through, its always nice to rub it in peoples noses when they say video games do no good.
Like Oniya said, it is free ware and does require a registration. You have to download a client (which is small if I remember correctly), and that can be used in on and offline modes. There are a handful of tutorials before you are tossed out, with an option to go back for more complex tutorials. There are various features you can manipulate, like the rotation of various segments, the placing etc, I didnt get into the really deep stuff before I lost interest. You can set various conditions like locking certain features into place or 'elastics' that pull segments together and then push a button to have the entire structure optimize itself. The goal is usually to try and get the highest score by manipulating small branches on the outside into the most desirable configuration, usually with the least space taken up.
I feel this game proves a point about a concept known as 'gamification'. Its where you take aspects of games and apply them to other things because, hey, games are fun right? A site where the more you participate, you earn credits which can be used to buy in site items or redeem them for real world things is an example. The ammount of man hours put into a free online multiplayer game, even if its just chat and a high score board like Foldit is staggering. I can remember the exact figure but since WoW released in the mid 2000s, players have already spent a few MILLION years worth of time playing.
What im hoping is that the rest of the world takes this to heart as a lesson and applies it to everything else. Incentive's things is great, and having a game to get those incentives is even better. The US Military has already adopted this in a project to help fight piracy in the Gulf of Aden, in the form of a simple game on one of their websites (the name escapes me).
I know this seems like a long post for an old topic, but I know a fair but about the subject xD