And generally speaking they worked "in the background". By that I mean away from the public. Industrial complexes, mines, and so on. Only two I can think of that were "famous" (sort of) were the B&O's little Joe (0-4-0T) and the PRR Class A3a (0-4-0T). Were there other wheel arrangements? Of course. 0-6-0T, 0-8-0T, and even a 0-10-0T (or two).
Cascade is correct - there were oodles, heaps, and gobs of them - just rarely seen and even more rarely photographed.
Ben