Fabrice Bellard’s PC Emulator written in… JavaScript

Um, this runs Linux within your browser. What?! You can try it out here.

The CPU is close to a 486 compatible x86 without [an] FPU. The lack of [an] FPU is not a problem when running Linux… because it contains a[n] FPU emulator. In order to be able to run Linux, a complete MMU is implemented.