Progg as in http://en.wikipedia.org/wiki/Progg. This is a Swedish band who were active between 1967 and 1969. They became quite popular world wide but went different ways and kinda faded away. (Bo hansson had a solo carrier) Hendrix have played with them in a club called Filips in Stockholm and decided to make a cover of their composition Tax Free. Check out their album called "Monument". Great stuff! Hope you like them!