It seems there are more and more cameras on the market these days. If you are booked in for a job on a camera you haven't used much, using a menu simulator can help you familiarise yourself with the layout of the menu systems before you get to the job. The last thing you want is to be fidling around scroling through menu pages when you should be shooting.
Sony F-65 simulator
Canon C300 Simulator
Below is a list of camera simulators, some can be used as ipad apps, others can only be used online.
Arri Alexa (available as an ipad app)
Sony F65 (this one is from the app store)