A Rollerbrake is a kind of drum brake.
The RollerBrake is cable-operated, but as with coaster (backpedaling) brakes, the braking surfaces are all metallic, and they are grease-lubricated.
The stationary part of a Rollerbrake is clamped between nuts on the axle of Nexus hubs. (Shimano Alfine hubs are very similar to Nexus hubs, but use disc brakes with Shimano’s proprietary CenterLock brake disc, affixed with lockrings similar to those used for cassettes.)
The Rollerbrake is most practical for urban cycling in areas without long, steep descents. Advantages are that is weatherproof and requires little maintenance. It also is replaceable as a unit — unlike other drum brakes which are inside the hub, so the hub, and as a practical matter, usually the entire wheel — is replaced if the drum is worn out. Several models of Rollerbrake of different sizes have been sold. Even the smallest Rollerbrake can skid the rear wheel of a solo bicycle.
Disadvantages? Only Shimano Nexus (internal-gear) and Nexave (cassette) hubs have fittings for Rollerbrakes. Only large Rollerbrakes with large cooling fins have enough heat dissipation for speed control on long downgrades. No Rollerbrake is suitable for use as a drag brake on a cargo bike or tandem. There have been reports of grease’s catching on fire during long descents! Overheating to this degree will require replacement of the brake, and rebuilding of the adjacent hub bearing. One more reason to carry a water bottle on your bicycle…