Total Commander

For example when you change the button bar, at the 'command' input-field you have a magnify icon, when you click on it you see commands category at the left.

Suggestion: add 'Environment variables' as an category, when user clicks on it all available environment are shown.
This is just an example, implementation is off course up to author (if worthy of implementation).

If you mean the environment variables listed when you run: hh.exe %COMMANDER_PATH%\TOTALCMD.CHM::env_vars.htm then I am all for it, but I think it should be assiged to a separate dialog, opened via the menu under the "Change >>" button as "Insert env. variable".

Yes that's the 'Environment variables' I was referring to.
I hope it will be implemented in some form.