Online games that are currently running. You can join!

• NationStates. Run your own country. Visit mine (also called Playce). Also, forums!
• Neal.fun. This is also demented and I love it.
• Pixel Cat's End. Reminiscent of Neopets. Adopt cats, send them on adventures, interact with their stories and lives. Registrations open every seven weeks.
• Riverton. "A nostalgic browser-based virtual pet/ranch sim." Horses! Currenly in beta.
• TamaNOTchi. Tamagotchi, but in your browser.