Tiny Core Linux
Tiny Core Linux is an extremely tiny Linux distro (~8MB) by Robert Shingledecker, the man responsible for one of the first mainstream Linux deployments in government (will update with details) — but more importantly, was one of the main developers on the very small “Damn Small Linux” (DSL) project, before a parting of the ways. He started the Tiny Core Linux (TCL) project, which while has some semblance to DSL, it is different (and much more useful) in design and real-life everyday use. It’s like a Debain (what Ubuntu comes from) in that it has a nice big ready-made software repository so you don’t have to compile software you want to run. However, it is not the Debian repo system, and you cannot run apt-get under Tiny Core (sorry, all you googlers).
In short, Tiny Core Linux is the ideal tiny Linux when you’re making tiny instances of “just enough operating system” systems, or JeOS boxes. Some call them net appliances. They can be virtual (tiny qemu-hosted servers on your desktop) or real hardware, like Raspberry Pi’s, or even the OS you choose in the cloud, although other projects like AWS AMI and CoreOS serve that niche a bit better, and it is the base distro that I chose to derive Levinux from. Levinux is really just Tiny Core Linux without the optional desktop (FLTK/FLWM) running on some very popular and stable versions of the qemu PC emulator. There’s some nifty scripts on the host side that get TFTP’d over to the virtual guest and executed inside the VM on first-run to initially configure the server.