For a short period of time a DOS emulator made its way into Apple's App Store. But don't all rush to the App Store looking for it, because Apple quickly had a change of heart and pulled iDOS from the store.
Some people were quick enough to get their hands on this 99 cent app:
This app probably broke about half of the billion or so of Apple's rules and regulations relating to apps, so it's a bit hard to see how this got aproval in the first place.
Shame it got pulled ... seemed like a really cool app.