Emacs :) A great operating system that needs an editor
I (and many others) have been thinking about a system that boots to Emacs. With the guile backend we might get enough speed to make it tolerable fulltime.
The only thing missing (and I bet somebody has done this too) is a way to run graphical ELF binaries with an embedded X/Wayland type thing.
Buffers being graphical, including the possibility to work with images inline Lisp Machine style.
The gdb integration was more ergonomic, felt closer to something like DDD.