Found while cleaning out the garage for Mom - a vintage ARCO circular saw powered by an electric drill. It has an adjustable/removable edge guide so that you can cut a straight line a bit away from a straight edge, tilts to 45° for bevel cuts, and has an adjustable depth of cut.
Measuring indicates that it uses a 4" diameter blade, which was not to be found in the stuff with this unit. It appears to have been made in the 1950's. I've included a photo of a Popular Science ad for a 455 unit, which is similar but uses a 5" blade rather than the 4" blade used by this unit.
The drive is free and works properly, as do all the adjusting features.
Asking $60. Where are you ever going to find another one?