Thiery,
You're right - not counting the 30mm distagon (fisheye), 40mm f/3.5 Super angulon, 40mm zeiss distagon, 50mm f/2.8 AFD, 50mm f/2.8 PQS, 50mm f/4 distagon, 55mm PCS (tilt/shift), 60mm distagon, 60mm curtaon, 80mm AFD, 80mm AF 2.8, 80mm f/2 xenotar, 80mm f/2.8 planar, 90mm apo macro, 110mm f/2.0, 120mm f/4 macro, 150mm apo macro, 150mm sonnar, 150mm tele xenar, 180mm f/2.8, 180mm AFD, 250mm , 300mm f/4 apo, 350mm, and 500mm - the rollei hy6 lens line up is incomplete!
Edit: Whoops forgot the AF 60-140, 75-150mm zoom, 140-280 zooms, the 1000mm tele-tessar and probably a few more.
While not just for the Rollei, you can mount things like imagon lenses (i used a 120mm imagon just yesterday to do portraits of a local singer who wanted a special look), and specialized macro lenses such as the M-componon's because Rollei has a shutter adapter. That's just one item of a long list of cool accessories that make the system so fantastic.
Shooters will be lucky to ever have a lens system as complete as that, as fast as that, and as high quality as those available for Rollei 6000 and Hy6 platforms.
Eric