Commander Keen is id Software’s early DOS platformer, and it’s become my standard test case whenever I want to learn a new porting target. It’s small, well-understood, and — via the open-source Chocolate Keen source port — genuinely portable, which makes it a good stand-in for “can I get real DOS-era code running on this platform” without taking on a huge project.
I’ve ported it twice for exactly that reason: to WebAssembly, as a way into Emscripten and browser-based porting, and to the PlayStation Vita, as a way into homebrew cross-compilation once the Vita’s h-encore exploit made that practical.
