What are some alternatives?
When comparing McOsu and Osu, you can also consider the following products
StepMania - Rhythm game for Windows, Mac, and Linux.
Clone Hero - Clone Hero is a free rhythm game, which can be played with any 5 or 6 button guitar controller...
Frets on Fire - Bonus content.
VOEZ - VOEZ invites you to embark on the remarkable journey of teenage dreams
Rocksmith - Rocksmith builds off of the fundamentals of music games like Rock Band and Guitar Hero by offering fundamental lessons in actually playing guitar.
BeatX - BeatX is a Stepmania/DDR for Android