ReactOS

A full x86 PC in WebAssembly, booting a menu of real operating systems from self-hosted disk images: FreeDOS (A:\> prompt), Windows 3.0 / 3.1, Windows 95, Windows 98 and ReactOS to their desktops, plus a small Buildroot Linux. Windows 98 and ReactOS resume from a pre-booted state snapshot, so they come up already on the desktop; Windows 3.x and 95 cold-boot from disk (give 95 a minute). Click the screen, then use the keyboard and mouse. Add ?debug, or click Debug, to inspect the live x86 registers, read physical memory, and step the CPU. Step runs one v86 time-slice (see the notes: a JIT-in-WASM core has no clean one-instruction step).