Aww, how about a C-64 emulator...
you could even offer an option to simulate "speed" when loading from  
"tape"
(avg time: 30 - 60min, chance of failure: 65% or higher)
Or even a PDP-11

Just be sure to include the frustrations of old, slow machines that  
often had problems, as an option to set. Can be very instructional to  
users who never had the experience and to those who start to wax  
nostalgic.