Could I also suggest Tiny Core Linux [0]? It still seems to be in active development, and the ISO which includes the kernel, shell, and window manager (FLWM, based off FLTK) weighs in at only 16mb in total. It's pretty impressive, and its good fun to play around with in a VM.
To learn about embedded/headless/obscure-hardware Linux I would suggest checking out http://www.linuxfromscratch.org/ instead or using a distribution like http://www.gentoo.org/ for awhile to get familiar with lower level concepts and building custom systems. Customize kernel options until things break, try at least one embedded platform, and build a PXE diskless boot system.
Ditto. Compile time was pretty killer. But between my years spent running Slackware then Gentoo, I feel like I got a good feel for the core of how Linux systems should operate (and the benefit of someone else running the builds!)
Another still actively developed alternative is SliTaz [0].
Comes in images from 45Mb for a working desktop down to a bootable floppy, rolling release, runs in RAM with no persistence by default, and uses a custom package manager that, outside of having its own decently sized repo, can convert packages from Debian, RPM, Slax, Puppy, Slackware, NuTyX, Arch, Alpine, OpenWrt, 0Linux, paldo, Void and Tinycore according to the manual.
Man, this brings back some middle school memories of back when my biggest USB drive was 128MB and I was playing with Linux live images for the first time. Sad to see why and how the project died.
I used this 15 years ago from a 128Mb USB stick. It was my introduction to linux and set the bar really high for responsiveness. I think I even installed Windows 98 second edition on a computer running Windows XP just to feel the same.
DSL hasn't been updated since 2012. But even when it was still under active development, they made the controversial decision that they would never ship 2.6 because it was just too big and bloated; and that all of the important bits would be backported to 2.4, because surely there were enough people sticking with 2.4 that it would be supported forever, right?
Every couple years these things get posted by people who have discovered then for the first time, and then get voted up by those same people or by people who have a fondness for it.
I welcome the up voting of these sorts of things. It's great to see projects with new eyes, and be reminded that not everyone has the same historical experiences that I've had.
Please don't submit comments complaining that a submission is inappropriate for the site. If you think a story is spam or off-topic, flag it by clicking on its 'flag' link. If you think a comment is egregious, click on its timestamp to go to its page, then click 'flag' at the top. (Not all users see flag links; there's a small karma threshold.)
I remember using DSL quite a bit back when I was first playing around with Linux. It was the only desktop-oriented Linux distro that seemed to actually run on my Compaq Presario 1210 (Tiny Core didn't even exist back then, and even when I did eventually try it, it choked on the laptop's weird graphics card). Pretty much nothing else was able to fit in the laptop's "whopping" 32MB or so of RAM (aside from Windows 2000 and older, as well as FreeDOS).
[0] http://www.tinycorelinux.net