Welcome to Linux running natively in your browser!
There's no x86_64/RISC-V emulation going on here, instead this is a port of the kernel to WebAssembly.
We've got a patched version of the Linux kernel running, complete with virtio devices, memory isolation, and multi-core support. For the userspace, we've ported BusyBox and Musl, and much more.
If this sounds interesting, you can check out the source at github.com/tombl/linux (the kernel) and github.com/tombl/distro (the userspace and this site).