Potluck (Windows/Mac, free) - Remember Very Pink Game from way long ago? One of the creators has gone and teamed up to make another cute, infinitely awesome free game called Potluck. Potluck stars a witch named Potluck who was having a potluck dinner with her witch friends. They went to play some volleyball and returned to find a demon had stolen their food! Walking through the moderately spooky world, you'll blast enemies with your witch powers and collect hearts to keep your health topped up. Simple, but so much fun.
Mr. Red's Adventure in The Missing Balls (Windows/Mac/Linux, free) - Mr. Red doesn't have any balls for his Christmas tree. That is, decorations for his tree. You're going to help him collect some! A simple platformer with a festive cheer, hop, jump, smack things with a giant candy cane and push a few blocks around as you explore several short levels in search of more ornaments.
Super Mario Eclipse (Windows, free) - A surprisingly complete fan game based on (what else) the Super Mario Bros. series. Eclipse isn't just a remixed Super Mario World, though. It's a fusion of a puzzle game and adventure platformer with some creative inventory and NPC features thrown in for good measure. The experience certainly looks like a Mario game, but it feels like something totally different.