The brand name of kart engines manufactured by BRP is Rotax.
Rotax engines are made by BRP-Rotax GmbH & Co KG, an Austrian company owned by Bombardier Recreational Products. The Rotax name covers a broad range of internal-combustion engines used in aircraft, motorcycles, snowmobiles, personal watercraft and off-road vehicles, as well as karts.
Rotax entered karting prominently with the Rotax MAX engine series. The Rotax MAX 125 is a liquid-cooled two-stroke engine designed to deliver strong performance while remaining relatively easy to operate. Its electric starter and centrifugal clutch helped make the engine attractive for recreational and organized racing use.
The karting line also led to the Rotax MAX Challenge, launched in 2000. It uses controlled engine specifications and sealing procedures to reduce performance differences between competitors. That makes the series a one-make-style competition even though drivers may use different chassis brands.
Rotax is often confused with BRP itself. BRP is the parent company; Rotax is the engine brand and manufacturer associated with BRP-Rotax. Briggs & Stratton and Honda also supply kart engines, but they are not the answer to this BRP-specific question.