mid-late 90s I created a GUI based on java applets and "image maps" which was an image with sensitive areas which called a function callback when clicked. With this I created a gui for a central heating controller with knobs and sliders only. If you do not require textual user input, use this to create a unique look, organic i called it, totally unconstraint by the gui widgets on offer. Edit: of course java applets are long unsupported but you can create something similar with Tk i guess.

A more realistic approach is to use an html front-end with a mojolicious backend. Html offers all the widgets you need plus it is the easiest to create custom widgets. It can be accessed locally or remotely by any browser, hence any-OS.