EYN-OS is reasonably capable, the latest official release has a pretty unique GUI that runs in kernel space, with applications interacting with it via syscall. The design itself is sort of based off the Tilix terminal emulator, but with its own flair.
I'd recommend building the dev branch from source rather than downloading the latest release, as the dev branch has some pretty significant changes that make it a bit more "modern". The dev branch currently opts for a more traditional taskbar, but if you want to try out the latest release and that experience also, be my guest.
To get started right away, just run "make qemu-debug"; that'll build, create an EYNFS image, copy the contents of "testdir" to it, connect a network device, and boot up a QEMU window, ready to go. It runs on a minimum of 4MB RAM (any lower and GRUB won't load it), and I have actually ran it on hardware before (some old DELL Optiplex, I forgot the exact model), although just with a ramdisk.
It's public domain software, feel free to do as you please with it! I'd love some contributions and forks, it's getting a bit tiring working on it all by myself (having to balance it with college and everything).
One very notable thing you can do now (from the dev branch), is run DOOM! There is an included DOOM binary (forked from the Linux doom source code, another repo of mine) that I've tested with the 1.9 shareware WAD of DOOM. It runs reasonably so for a 386 of the time, however it only takes mouse controls, the keyboard doesn't really work on it (and to be honest, I'm not quite sure why).
Porting your favorite UNIX software should be near enough trivial thanks to my (albeit basic) X11 translation layer. While EYN-OS is not UNIX-like, I've made it as easy as I can to port software to it whilst still keeping it unique.
There's a custom image and video format (sort of broken in the dev branch, though I know they work with the release build) too, with an audio format in the works!
If you want to just try it out or even consider contributing, please do so here! https://github.com/KianGentry/EYN-OS/tree/dev