Depends what you want to know!
Marx did at least a couple generations of cars, none of which were very interesting! The first ones were two Vanwall like F1 cars, in about 1/40 scale, made in Hong Kong. Cute, in a toy-like way.
Then they went to a more 1/30 - 1/32 scale, but with very boxy sports and Indy cars, with a reduction geartrain if I remember correctly. The pickups were set much further apart than all other 1/32 sets so they weren't compatible with anything.
They did do, however, a very Dali-like Maserati Birdcase and Ferrari sports car, which had a little more character than the Indy and other cars (Mercedes, E-Jag, etc.). Some of these came with a gadget on the gears that made "engine" noises...
They were pretty widely distributed because of the Marx name, and because they were also sold under the Sears brand (as was Strombecker and maybe a few more brands).
Marx also did HO sets, and one in 1/24, which is pretty widely sought because of the wider track. The cars were a Ferrari GTO and Chaparral 2, not very well reproduced, but better than the 1/32 models. They also did a 1/24 Lotus and Ferrari F1, which I find interesting just because they're there!
hope that helps
Don