Ember tetras are nano fish like no other, they are the colour of fire and yet don't live up to that at all. in fact they are rather lazy, and perfectly happy bimbling about in a little nano tank. They do need company though so be sure to stock them with at least 6 member of their own kind.
They are perfectly safe to keep with any other nano fish so long as they are not aggressive, just be wary keeping them with large fish as an ember tetras would make a fine snack.