iDOS is a DOS emulator for iOS. It a port of DOSbox for iOS. The app includes Wolf3d, Duke I/II, Major Striker, SuperNova, and Kingdom of Kroz II.
The app originally snuck on to the App Store, until Apple removed it (oddly enough, it is still downloadble from the Congolese App Store). The developer moved the app to Cydia after that, and worked on it there. Unfortunately, the developer got distracted with a PC emulator, Aeumla, and abandoned the project.