Boxer is a free DOS game emulator for Mac
Boxer is still based on the DOSBox emulator, but as you've undoubtedly gathered by now, adds its own secret sauce into the mix. It lets you run DOS programs straight from Finder, and wraps your games in game boxes that launch like Mac apps. Boxer allows you to focus solely on playing, not requiring you to struggle with hard to understand settings or DOS prompts.
The latest version is 1.0 RC 2, and it works on Mac OS X 10.6 and 10.5. If for some reason you're still stuck on Mac OS X 10.4, there's a version that will work on that, albeit without all the bells and whistles of the latest release.
Speaking of which, Boxer 1.0 has undergone a complete redesign, and is now faster and more stable than before. The game importer is smarter, clearer, and easier to use, while the new Inspector Panel lets you instantly tweak settings while you play. You can choose your favorite rendering style, make your game boxes prettier with cover-art from Boxer, and drag-and-drop folders and disc images to mount additional drives in DOS.
Boxer comes with four ready-to-play DOS games: Commander Keen 4, and demos of Epic Pinball, Ultima Underworld, and X-COM: UFO Defense. The developer's website also has a nice section that helps you find both free and commercial DOS games. That's where you can, among other things, find a demo version of Star Wars: Dark Forces. A screenshot of this game running in Boxer is available after the break.
Download Boxer for Mac OS X