In the past, I have developed several 6502-based computer simulations. I have lost the source over the years to many of the incomplete projects, but a kind soul has returned to me the Apple I emulator that I wrote back in 1999. This was based on earlier work with vPCB which emulated the arcade hardware of the games Centipede and Millipede. This was all back in September of 1996, before the MAME juggernaut took over the scene. The Apple I emulator has been updated a little using SDL so it runs on modern hardware/Windows. vPCB for DOS is lost forever, but the project has been revamped for the Palm platform.
Download Windows/SDL version here.