The Rockson ADY-120 has 2 mono 1/4" (TR) plug on one end, and a 1/4" stereo (TRS) jack on the other. Among other uses, with a short TRS patch cable (which I also happen to have for sale), you could go from an effects pedal that has left and right mono outs to a pedal that has a TRS stereo input, or vise versa.

This new, still in the packaging, never used. The female jack style is different on a couple of them (see photos 3 and 4). The model number is the same, so I assume that the function is. Unless you make your preference known, you'll receive whichever one I grab first.