If you've ever tried to play a classic old DOS game on a modern PC then you'll know that the results can be, well, variable. The graphics may fail, the sound might not work, the game speed is often too fast or slow, you may have unexpected crashes - or in some cases the game won't start at all.
The solution? Install DOSBox. It's a full x86 emulator, which means it creates an environment that fools old games into thinking that they're running on the kind of ancient hardware they were designed for. Most will run much more reliably as a result, and if there are problems reported then the DOSBox team will regularly tweak the program to add specific game fixes and support.
What you're getting, then, is something that's actually better at running old programs than the original versions of DOS. And yet, because this is an open source project, there's no need to pay for a licence and it won't cost you anything at all.
Unfortunately the very nature of DOSBox is that it's emulating DOS, so launching the program leaves you at a somewhat unfriendly command line prompt. There is a manual to help you figure out what to do next, but if you're still struggling then you may benefit from installing a DOSBox front end, a program that adds a graphical interface to the program and makes it easier to use. Check the DOSBox download page and browse the Frontends section to see what's on offer.
An essential tool for anyone who still loves playing classic DOS games. And if you've no idea what we're talking about, check out a site like DOSGAMES.COM