DOSBox is a multiplatform, command-line DOS emulator.
DOSBox is capable of emulating many older computer games that are otherwise very difficult if not impossible to play on modern operating systems and hardware. It has very high compatibility, as it can be configured to emulate the environment of many machines, with support for various display modes, including CGA, EGA, Hercules, Tandy, and VGA. With some work, it is even possible to install and load old Windows operating systems, such as Windows 3.11 and Window 95, thus potentially being able to play games made for those platforms.
This is an enhanced build of DOSBox by ykhwong, with support for Direct3D and HLSL shaders, Glide, ethernet, and many other features not found in the official version. Unlike vanilla DOSBox, it has a menu for on-the-fly configuration. Highly recommended.
A great frontend which allows custom per-game configurations to cut back on fiddling with settings just to run specific games well. It also lets you use your own build of DOSBox instead of the one it comes with, so it can be used in conjunction with DOSBox SVN Daum.
There has been interest in creating a version of Dosbox that incorporates compatibility with Windows 95/98/ME. As of 02/09/13 it has not passed the theoretical stage and no work has been done.