osu! is a free-to-play game based on a variety of popular commercial rhythm games. While keeping some authentic elements, osu! adds huge customisation via skins/beatmaps/storyboarding, online rankings, multiplayer and boasts a community with over 100,000 active users! Play the way you want to play, with your own music, and share your creations with others.
The latest, as of 7/5/12, version of osu!, the rythmn game based on games such as Elite Beat Agents, by ppy. This version adds a streamlined start-up operation, such for easy and quick access.