iOS: As we grow older and have more commitments, it becomes harder and harder to get friends together in one place to watch a ball game or play video games. Xbox Live and PSN help take care of the latter, but how about the former? If you don't mind holding an iPhone the whole time, there's PlayUp.
PlayUp's idea is chat rooms where you and your friends — or even you and strangers — can text-chat-discuss a game as it's going on. It's something you can easily do now with any IRC room or Google Hangout, but where PlayUp stands out is that they know every single game that's going on in many sports, from soccer to football to baseball, to ridiculous ones like Australian football and cricket. (And I mean ridiculous in the most endearing way possible.)
Once you log in, either through Facebook or their proprietary account, just join an existing room or make your own, then get to chatting about New Zealand is totally going to beat France in the Rugby World Cup finals.