Are there any demos that run on PC platforms that aren DOS-based?
Only two that I know of: An OS/2 demo has been written for OS/2 3.0 (OS/2 Warp, with MMPM/2 extentions installed) called Peripheral Evolution OS/2 by Ethos. It also comes with its own source code. A demo for Linux also exists, Hard Rox by Skal. It won the Wired ’96 demo competition, and it runs in DOS as well. There is a ongoing project to create an operating system exclusively for writing demos, called the DemOS project.