What are some alternatives?
When comparing McOsu and Frets on Fire, 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...
Rocksmith - Rocksmith builds off of the fundamentals of music games like Rock Band and Guitar Hero by offering fundamental lessons in actually playing guitar.
Osu - Osu is Music, Rhythm, Single and Multiplayer video game developed by Dean Herbert.
VOEZ - VOEZ invites you to embark on the remarkable journey of teenage dreams
Audiosurf - Audiosurf is a music-adapting puzzle racer where you use your own music to create your own experience.