Depending on the source this is called a Sighinolfi BMW 750 barchetta from 1953 or a Nardi Sighinolfi from 1953. It's for sale right now, text from the website:
Sergio Sighinolfi from Modena was a respected works-driver for Stanguellini and Scuderia Ferrari. He started making his own etceterini racing-cars in 1953. This one-off car was his 3rd car and was made on a Nardi Danese modified tubular Gilco chassis with a Nardi-Danese modified 750 cc BMW boxer-motor. Carrozzeria Campana from Modena made the bodywork.