"The only time it doesn't fit great is with e.g. GIMP that has several small windows for toolboxes and stuff" You could try running GIMP in single-window mode

"The only time it doesn't fit great is with e.g. GIMP that has several small windows for toolboxes and stuff" You could try running GIMP in single-window mode (via GIMP's menu option: Windows -> Single-Window Mode). It doesn't get rid of every little window GIMP has, as it'll still pop up windows for saving files, for example, but it's much better than multi-window mode, if you don't want to bother with lots of little windows.