"rFactor" is an evolution of "F1 Challenge '99–'02", but without the licensing of Formula One circuits and teams. As such, "rFactor'"s initial release only included four fictitious circuits (seven as of v1.087), with about a dozen layouts within these facilities and there were about six vehicle classes, including two open wheel and four sedan classes. Among its most notable features was a rich interface for creating custom game contents, which made it possible for amateurs to create additional vehicles and tracks for the game. On August 1, 2006, ISI released the full update, with many changes and new features, including the new 2006 BMW Sauber F1 and a much requested manual. Another notable and often requested feature was driver-swapping, which allowed to change drivers during the race, enabling up to 24 hour events like Le Mans.