This Electrically Powered Train Set by Marx utilized the zig zag cars and engines but each car was equipped with wheels so it could operate on track. Marx didn't miss a trick!
The battery operated engine is the same No. 66 used in some of the zig zags but now fitted with flanged wheels approximately HO gauge. This boxed example is the Marliner.

Luxury Lines Zig Zag

Here is another example of the set above. This one is lithographed as the Luxury Line. I wonder how many other versions of this are extant.

This Marville Local represents a larger rendition of the zig zag train which was also designed for track. The car wheel sets are typical postwar plastic with metal axles as used on clockwork tin sets. The engine number is 3 which is certainly in line for Marx (3, 333, 66, 666, 1666, 999, 1998). I have another example of this set (stored with my plastic) called a "Guide-A-Train" which has some curved plastic corners that can be strategically placed to guide the train around a room without track.

This is another little tracked train toy that must have been very popular considering how many show up on eBay. The train is a one piece molded plastic contraption with wheels only on the engine. The caboose has a dog which fits down between the rails keeping the rear of the train nominally on the track. The plastic tree in this set had only 12 sprues for the molded signs however there are 16 signs and posts. I bought the set as is. Maybe someone added some items.