I think it's oddballs cause the only other thing is livebearers (they are related too guppies) but they lay eggs so oddballs. Please don't bite my head off for saying killies are related to guppies, because in my book they both come under 'Tooth carps'.
Threadfin rainbow fish are wait for it.............rainbow fish Sorry, theyre not killies they are members of the Melantaeniidae group of fishes. Like most rainbow fishes they are reasonably hardy and easy to keep, they preffer neutral to slightly alkeline water and need a tank with tall plants to feel secure.