New York - A number of former executives from SpiralFrog, which is developing an ad-supported legal media download service, announced on Monday the formation of Rebel Digital, a new advertising consultancy focused on the digital music space. Rebel Digital's management team includes former SpiralFrog CEO Robin Kent and chief marketing officer Lance Ford. The company said it has signed Qtrax -- which is also developing an ad-supported music download service -- as its first client.