these small tanks are totally worthless, some of them cost even more than a standard 10 gallon. If you ask me, anything smaller than 10 gallons deserves to be holding punch in the freezer, not a bunch of fish. I'd understand if they were small and cost effective, but a lot of them are either plastic boxes of the same quality as a plastic cup, or a fancy designer doodad which costs more than a standard tank over twice its size.
In regards to fish for tiny tanks, shrimp, endlers livebearers (I suppose, they're not "schooling fish" but they are social, let's not forget.) and well, that's all I can think of, would really be comfortable in such a set up.
It's really unfortunate how so many fish are improperly kept, most people don't even know what they're like at their full potential, and therefor think their fish are happy in a small tank, even if they're just holding on because that's basic instinct.
if you want to see that fish at its best, in its best color, best activity, best health, you should really just get a proper sized tank. Or if you just like the looks of small planted tanks, then get a small planted tank. Just don't put anything but plants in it.