Well, we can rule out the Mollies, as they're livebearers... It's unlikely to be the black neons, as characins seldom breed in an aquarium env. without environmental changes/triggers. BUT, danios are egg-scatterers (on the bottom, non-adhesive eggs).
What kind of snail do you have? They don't look like the eggs my Gold Inca Snail lays, and they're not the jelly-like masses that most snails lay...
***If it's the black neons: the eggs would be partially adhesive on leaves, but would hatch within 36 hours according to all the sites I've visited.
http://badmanstropicalfish.com/profiles/profile51.html is one of them
***It it's the danios: the eggs should hatch within 48 hours (sites have conflicting info).
***If it's the snails: the eggs will hatch within 4-6 days probably.
So, this is a conundrum. I'm guessing the black neons for now, though I know they seldom spawn in an aquarium. Keep an eye on the eggs! You may want to remove them to a separate tank, as they'll already be fertilized by now.
HTH, though I know it doesn't really!
