HelenOS
One of those operating systems that is used for operating system research here and there. I think that's also what it was made for. The last releast was earlier this year, which makes it seem one of the more actively developed research OSs. With the release there are also prebuilt ISO for a variety of platforms including the usual, Raspberry Pi, other ARM platforms and older PCs.
There are similarities to UNIX-like systems but it is clearly not a POSIX system. Basic utilities are included as well as some basic console and graphical applications and demos. I didn't look for any additional software, yet. I'm not sure if I will use this os much more. But by booting flawlessly without any changes and effort, this is one of the more usable OSs I've tried. So I might. It has network capabilities, a basic GUI and TUI, window manager and its own shell.
The GUI is optional. Most applications run in the console mode as well, which is a TUI that mimics the GUI with its start menu. Which is good to have because the GUI is really slow to the point that the mouse pointer is lagging behind.
On my desktop PC neither a PS/2 nor a USB mouse worked. But the touchpad in my old latitude worked fine, including the second set of mouse buttons that work in almost no OS. Graphics mode worked with the appropriate resolutions automatically. Above that I haven't tested any hardware.
There are screenshots in the official wiki.