Nano Pets were released by Playmates in 1997. Of the Big Three of the 90's virtual pet craze, Nano had the smallest variety and were not as well spread as Tiger's Giga Pets or Bandai's Tamgotchi, but were the only to feature a baby in their lineup.
Nano Pets only released 3 lines of their pets - Original, Talking, and Fighters, with the Puppy Family being a one-off.
The Nano Puppy, Kitty, Baby, and Dino each have two shell types - transparent and opaque - while the others only have the opaque shell.
Nano Puppy Family
The Nano Puppy Family is unique, letting you raise both a male and a female you can connect and get puppies from!
I could not find instructions online. If you have them and can scan them, please contact me!
Talking Nano Pets
The Talking Nano Pets were the second version of Nano Pets, being much larger than standard and featuring voice acting! Each of the three pets will talk to you, and gameplay is largely the same between all three.
They're also unique in that instead of a character walking on the screen, the screen is entirely your pet's (or baby's) face!
These also have two types of shells, very similar to the original versions of each.
Talking Nano Puppy
Talking Nano Kitty
Talking Nano Baby
Release in 1997, this was Playmate's response to Digimon. There are only three versions, and all have near identical play, with the only differences being the sprite and sound effects. Like any other battling pet, you can connect two together and duke it out.
Nano Racers are kind of a mysterious pet. There's no good source of information on them, and I could find no instructions. All I could find is what Tamenagerie.com wrote up, saying you build a car and then race them. There seems to be a few colors, but they all seem to be the same programming.