Volvo Flywheel Hybrid System (aka KERS) Tests Completed Successfully: If you follow Formula One
In F1, Williams was developing a flywheel KERS (kinetic energy recovery system), but never raced it in F1. They ended up doing a battery based KERS system like all of the other teams. However, Williams has licensed this technology to be used by Porsche and Audi in Le Mans style sports car racing. Williams is also working on other applications outside of racing with their side business "Williams Hybrid Power".