Instructions: "be a cat." This is all you need to know about VVVVVV creator Terry Cavanagh's free and cannily-named mini-MMO, ChatChat. Go on, be a cat. Do what cats do (bum-licking not included, mercifully). Hang around with other cats in the way that cats do, i.e. doing your best to ignore them with barely-concealed hostility. Catch mice. Leave dead mice as gruesome offerings to your owner. Be completely unmoved by the discovery of treasure, because if treasure doesn't run away, scream and bleed, what possible use is it to you?
No, there isn't crafting or raiding or or bosses elite items. It's a game about being a cat. When did you last see a cat wearing a mystical hood or worrying about what level it was? Pfft. Miaow and purr and nap and explore and hunt and be a cat, stupid.
In passing, I've been kicking around ideas for a puzzle-based cat sim myself for a while now, so it's vaguely distressing that someone else has dabbled in similar territory there before I could talk myself into doing anything. Still, it remains fertile territory - one day I'll find a programmer and empty my cat-obsessed brains into a game project.
Play ChatChat in your browser for free here. Oh, and if you don't like cats, you could always figure out the secret way to turn into a dog...