From Minor Studios:
Atmosphir is an online video game where you can play and design your own adventures. Anyone can become a video game designer with Atmosphir. Even if you don't know the first thing about game art, programming, or music, you can still make fun and compelling worlds. Using a simple design editor, building is as easy as stacking building blocks on a grid. There are hundreds of gameplay pieces to add to your creations, from basic ground platforms to treasures, enemies, and powerups. Build run and jump platformers, action-adventure combat levels, puzzles, racetracks, 2D sidescrollers, multiplayer arenas, or whatever you can imagine! When you're done, upload your hard work to Atmosphir.com, where other community members can play, rate, and comment on your level. With hundreds of new levels being uploaded every day, there's always something fresh and exciting to play in Atmosphir. Everyone can find something fun to play: from beginner tutorials that teach you the basics of playing, all the way up to brutal experts-only dungeons. Levels are incredibly varied - one minute you're playing a gravity-shifting sand castle, and the next you're climbing an 100-story treehouse. Earn experience points to level up, increase your rank, and win special attacks. You can also customize your character with a wide variety of weapons, outfits, dances and taunts using the paid "atmos" currency. The optional "Player's Club" gives you exclusive presents, 5x the experience, and 500 atmos a month.