Hi ... I saw the following in the MIT V8 thread
To me it looks like a chain tensioner attached to the end of the tension pulley. Since it's a Brompton clone, I assume it's needed when the bike folds given that the distance between the derailer and crank decreases.
However I imagine that it could have other uses as well. The derailer in the picture might be a short cage rear derailer to minimize the chance of striking something on the ground. The additional chain tensioner could pick up additional slack from the length of chain needed for the triple.
Does anyone know what that thing is and where one might get one?