-A small school of the smaller cories (?) and a betta...
-3 african dwarf frogs and a betta...
-Some type of killi? I know nothing of them but I know you can keep some types in a smaller tank
-A paradise fish
-3-4 platies OR guppies OR endlers (you can probably have more with endlers because they are so small)
-A school of 6 neons or any other smaller type of tetra (it would be "overstocking" it by 1" but they don't produce much waste)
You could also add a small snail in any one of these setups...
I was under the impression that tetras needed to be in atleast a 10 gal tank, preferably a tank that is 24" long because they are very active and need the swimming space.