2600 wrote:
I thought I heard that the Everdrive N8 might of used it at one point, but don't know the details so correct me if I'm wrong. Do any other NES Carts use the the System Clock?
I don't think that any cartridge that ever was meant for use by the public uses the System Clock line. Any cartridge that needs a clock can obtain a 1.79MHz clock from M2. M2 is also used for sychronization with the NES CPU. The EverDrive N8 exists in both NES and Famicom pin versions, and the Famicom does not provide a System Clock line.