The transmission package (the transmission:gui output specifically) has transmission-gtk, but I personally prefer transmission-qt. By including qtbase, qttools, and qtsvg, transmission-qt will also be built.
I've made a simple package that inherits from transmission to do this: (define-public tranmission-qt (package (inherit transmission) (name "transmission-qt") (inputs (modify-inputs (package-inputs transmission) (append qtbase qttools qtsvg))))) This works, except that transmission-qt.desktop is moved to the gui output due to the inherited 'move-gui phase. I could figure out how to remove that phase to fix that, of course. But I'd prefer if transmission-qt were an option for the transmission package directly, either under a new :qt output, or to have both transmission-gtk and transmission-qt under the :gui output. Or just a separate package, transmission-qt. Any thoughts on that?