Wikipedia
DOSBox is an emulator program that emulates an IBM PC compatible computer running a DOS operating system. Many IBM PC compatible graphics and sound cards are also emulated. This means that original DOS programs (including PC games) are provided an environment in which they can run correctly, even though the modern computers have dropped support for that old environment. DOSBox is free software written primarily in C++ and distributed under the GNU General Public License. DOSBox has been downloaded over 30 million times since its release on SourceForge in 2002.
DOSBox can run old DOS software on modern computers which would not work otherwise, because of incompatibilities between the older software and modern hardware and operating systems.
A number of usability enhancements have been added to DOSBox beyond emulating DOS. The added features include virtual hard drives, peer-to-peer networking, screen capture and screencasting from the emulated screen.
An official version of DOSBox has not been released since DOSBox 0.74 in May 2010, although development continues in the SVN version. Forks such as DOSBox SVN Daum and DOSBox SVN-lfn provide additional features, which include support for save states and long filenames (LFN).
A number of vintage DOS games have been commercially re-released to run on modern operating systems by encapsulating them inside DOSBox.