I worked on a bunch of different prototype at Bigpoint none of them ever saw the light of day as far as i know.
I made a variety of different "fake-mock-up-screenshots" or "Vision-Pictures/Concepts" based on the ideas of our game-designers.
One mobile game with the working title "Warfleet" (ironically no longer based on naval units but tanks at this point) had an extended pre-production phase were some models textures and fx got created but it was ultimately canceled.