Can someone familiar with this explain what it is? I've read the guix page and it's a package manager - so is this a graphical or command line tool to do UK government stuff (with no screenshots)? Or something else?
Guix 1.0 was released just two months ago. The announcement summarizes what it can do for you in these areas: https://guix.gnu.org/blog/2019/gnu-guix-1.0.0-released/ .