Definitely the opposite of "light", but you mentioned chess and if you're into something similar but very different, you might try learning #Go together on online-go.com. That site has a very short introduction into the game under the Learn tab, but it only covers the very basics and initially you will have no idea what you're doing. The rules are simple, but there is a lot of complexity that arises from that and professionals study the game for years. But even as a complete beginner it's fun. Full on 19x19 games can take a long time, but games on a 9x9 board are fairly quick, comparable to a chess game.

Still, this would be a journey. If you want something not turn-based and relaxing to play while chatting maybe try something else but I can't give any recommendations.