Fret on Fire is a PC game that plays similarly to Guitar Hero. It is for free and includes a Song Editor, so you can transpose your band´s promising demo tape or whatever James Blunt tune you´ve been whistling for the past week.
I´m glad games like this are made for many reasons: First, I´m an amateur musician (or something close to that), so I enjoy watching this universe as video games settings. Secondly, the fact you can use it as a tool to actually create songs and share them in a different way. Also, the rhythm/melody based gameplay is an interesting one.
I haven´t played FoF yet so, if you have, let me know how it feels like.