It was a shot-lived rangefinder option – maybe because it was too modern. The Contax G System consisted of two cameras and seven lenses. This article gives an overview of history and product range.
The M Files jubilee marks 20 episodes of a unique Macfilos series. It covers third-party lenses, cameras and accessories with Leica M-Mount. Read here why these articles could be useful for you
This review covers two Carl Zeiss Contax Planar lenses that were originally made for other camera systems but converted for Leica M Mount: The Planar 50/1.4 by Skyllaney and the Planar 45/2 by Funleader.