Are you old enough to miss the vintage DOS games like Dangerous Dave, Digger, etc. that won't run on a modern operating system like Microsoft Windows or Linux? If you do, you don't have to. There is a little cool free software called DOSBox that lets you run MS-DOS programs on your modern operating system.
DOSBox is an emulator that emulates an IBM PC compatible computer running MS-DOS. As a result, you can run MS-DOS programs including the old games that were written for MS-DOS environment. It can be downloaded from its download page and installed. On Debian, Ubuntu or similar Linux systems, DOSBox can be installed simply by running the following command:
aptitude install dosbox
Once it is installed and run, it displays a Z prompt. Now, you may mount any directory on your computer file's system as a drive on DOSBox. For example, if you are on Windows and you want to mount a folder called C:\Games on DOSBox, you need to execute the following command at the Z prompt in DOSBox:
MOUNT C C:\Games
It's no different on Linux as can be seen in the screenshot below.
Once you have a C drive, you can can use DOS commands to move from one directory to another and execute DOS programs just like you would do in a real MS-DOS system. Press Alt + Enter to go into and out of full screen.
The old DOS games can be downloaded from one of many websites on the web that maintain an archive of these games. DOSGames.com has a good collection.