When I'm winding down at night, or just need a break from life - I love getting lost in puzzle games. Panda Poet is awesome because it's a combination word/strategy game, with relaxing music and lots of adorable pandas!
(Source: Lost Garden)
You can invite friends to play against you, or hop on a local match (which is usually what I do). There's also a small chat box on the left side if you feel like chatting up your opponent. I do recommend going through the tutorial as well. Even though it's a pretty simple game, half of the game is stealing your opponents pandas - which could be a bit confusing for new players.
The other thing I love is that the games can continue for a long time. If you only have five minutes to play, no big deal - your game will be saved and you can even receive emails when it's your turn to play, if you wish. I like to have about ten games going at all times, so there's always a game for me to come back to. And if you have a great game with someone, you can challenge them to a rematch after the current game is done! Awesome.
I play as CardiganNoir (firstname.lastname@example.org). If anyone's interested, I'd love to battle you with words! ^-^