This boots Tiny Core Linux and Debian on v86, an x86 emulator compiled to WebAssembly. Tiny Core runs Linux 6.12 on i686 with a busybox userland. Debian is a minbase 11 (Bullseye) rootfs on i686 with the 5.10 installer kernel, booted directly with no BIOS-level bootloader, which is why it starts so much faster than the ISO. Everything runs on your machine, nothing is sent anywhere, and the disk lives in memory, so closing this page destroys it.
Click boot to download the OS and start the machine. Tiny Core is 19 MB and takes about 36 seconds to reach a prompt. Debian is 35 MB and takes about 8 seconds, because the kernel is booted directly instead of through an ISO.
You get a shell: ls, ps, mount, cat /proc/cpuinfo, vi, the usual busybox set. What you do not get is a network, so no ping, no package installs, no curl. However, in Debian, tools like dpkg and offline apt-cache search work natively. You also cannot run containers or a Kubernetes cluster here, because an emulated machine has no nested virtualisation. For anything from my writeups you want Docker, so either a laptop or Cloud Shell, which is linked from the tools page.
While the machine runs it emulates a processor, which means it burns a real core of yours. It starts only when you ask, pauses when you switch tabs, and is destroyed when you leave the page.