This nifty website utilizes v86, one of the most impressive software projects I've seen in a while. v86 enables x86 emulation inside a browser. This allows you to run common desktop programs, or even entire operating system like Arch Linux, inside your browser.
In practice this does however with its own set of limitations and only works with x86, not x86_64 applications. But hey, archlinux32 runs inside of it (if only very slowly).