osu! is a freeware rhythm game developed by Dean “peppy” Herbert, originally for Microsoft Windows. The game has also been ported to macOS, iOS, Android, and Windows Phone. Its game play is based on commercial titles including Osu! Tatakae! Ouendan, Elite Beat Agents, Taiko no Tatsujin, beatmania IIDX, O2Jam, and DJMax.
osu! is written in C# on the .NET Framework. On August 28, 2016, osu!’s source code was open-sourced under the MIT License, the game’s assets are under the CC BY-NC 4.0 Creative Commons license. Dubbed as “Lazer”, the project aims to make osu! available to more platforms and to provide transparency. The community includes over 10.9 million registered users and 7.0 billion ranked plays.