DOSBox

Electrobody here I come! And Golden Axe! And Eye of Beholder!

Very portable and versatile. The documentation is not very good for comands like mount and imgmount, but the user can workaround this with a simple search. It's not 100% compatible with everything written for DOS, but surely runs a lot of games without any problems, even when two different sound cards are enable (e.g. a SoundBlaster and a Gravis Ultrasound). If you are running into problems, change the settings related to the core (e.g. try core=dynamic).