iDOS is an emulator for iOS devices that allows you to check out the early days of PC gaming.
There are six DOS games in iDOS, including the iconic Wolfenstein 3D. Games can be accessed from the library, and you can also use the DOS command screen, for PC purists.
Tap the top of the iDOS screen, and you can choose a floating PC keyboard, joypad, joystick or even mouse control. As with many iOS apps, these virtual controls are not great substitutes. iTunes file sharing has been disabled, meaning adding your own DOS programs isn't easy any more.
The games included have all aged a lot, and platformers like Duke Nukem never really stood up against the Marios of the world. Wolfenstein 3D isn't much fun today, and has been available on so many platforms over the past two decades, having it on iOS is nothing special.
iDOS is really only attractive to people who like the idea of playing around. It requires at least an iPhone 3GS to run smoothly, and even then you may find games suffer slowdown occasionally.
iDOS is hampered by the disabled iTunes file sharing and awkward controls. Emulating a old PC on iOS may be possible, but it's far from a match made in heaven.