The iDOS app, that was pulled from the App Store a few months ago is back. But this time there are a few changes made to it that might have helped it to get the approval to get into the App Store. Those exceptions have made the app a little less appealing. The app allows you to play original DOS games on your iDevices and previously had a nice option called iTunes file sharing which allowed you to run any game, but things are different this time.
iDOS now comes with 6 legal freeware games including Wolf3d, Duke I/II, Major Striker, SuperNova, Kingdom of Kroz II, which are owned by 3D Realms(Apogee Software, Ltd.) and now supports full virtual joystick/d-pad, and the ability to play in portrait mode on the iPhone.
Surprisingly the game still has the open emulation hack so you can use iPhone Explorer to open iDOS folder and place your own files in the documents folder, These files are at /Apps/iDos/documents/ that is the equivalent to C:\ inside of iDOS. This does not require you to be jailbroken.
You can download iDOS app from the App Store for free
Update: Sorry guys iDOS App for iPhone is now pulled from the App Store….Thank you Mikel in the comments