The shelter game
Every cat is looking for a home. See what it is like (how active it is, how much it meows, whether it gets on with children, other cats or being alone) and choose which of the three homes it would be happiest in. Getting it right means finding it a home. It is exactly what this whole site says: the perfect cat does not exist, but the one that fits your life does.
More things to do
An educational tool from Michipedia. It gives estimates, not a diagnosis: for anything to do with your cat’s health, ask your vet.