Is There Much I Could Keep In A 7 Gallon?

[dwarfgourami]

There are non-oddballs, too, of course:

microrasboras
heterandria formosa and other titchy livebearers
the smallest pseudomugils (like gertrudae)
sparkling gouramis
pygmy corys

African dwarf frogs
shrimps

I kept heterandrias in my 8 gallon until it sprung a leak, and that was a lot of swimming space for them; we are talking fish that are a third of the size of a guppy, if that, and produce a minimum of waste.