The dingle is a rare breed. This bike I saw was an Independent Fabrication cross bike with horizontal dropouts and S&S travel couplers. Sub note here, if you can race cross on a bike with travel couplers, they should be pretty much bomb proof. Anyway, this bike is a double gear ratio single speed. Hence the dingle name. You can rig it up in either of two gear ratios, one being lower than the other, but both requiring more or less the same chain length. It does require you to loosen the axle nut to get some slack on the chain, so I don't think this guy is shifting during races. Why build a dingle bike? I read an article by one guy who had to ride downhill to work and uphill and into the wind to get home. This reminds me of my bike commute in Boulder which was East (downhill and down wind) in the morning and West (uphill and into the wind) in the afternoon. Why not put a shifter on you ask? Well, winters in Boulder are kind of hard on drivetrains, and I'm sure the East Coast or central Europe is worse. Also, you get rid of cables which really do not like gritty road spray. Could be of benefit to single speed racers too. It allows you to pick the better drivetrain for the course once you get a chance to pre-ride it, unlike a true single speed setup that requires a tool-intensive cog change or money-intensive rear wheel change.
On as historical note, this reminds me of the original Campy suicide shifter: