DOSBox emulates an Intel x86 PC, complete with sound, graphics, mouse, joystick, modem, etc., necessary for running many old MS-DOS games that simply cannot be run on modern PCs and operating systems, such as Microsoft Windows XP, Windows Vista, Linux and FreeBSD. However, it is not restricted to running only games. In theory, any MS-DOS or PC-DOS (referred to commonly as “DOS”) application should run in DOSBox, but the emphasis has been on getting DOS games to run smoothly, which means that communication, networking and printer support are still in early development.

via DOSBoxWiki.

Not sure if I’ll ever need to use this but it’s nice to know it exists.  I read that they even ported this onto an Android platform.  I encountered DOSBox from this slashdot article.  Someone is running Windows 3.1 on their Android tablet so they can run a 1996 version of  Photoshop.