* 10-15 dwarf tetras (ruby or ember, for example) or microrasboras (galaxy, emerald, merah, brigittae, etc) of one species
* 1 Betta or 1 male dwarf gourami or 1m 1f Pseudosphromenus dayi or something similar
* 6-10 dwarf/pygmy rasboras of one species, or shrimp if Betta or gourami has good temperament
Or, if you wanted something different - you could look into some African Dwarf frogs - you could have a whole colony or up to 2 african clawed frogs depending on the dimensions of the tank