Tokens are like bitcoin just that they are created on an already existing blockchain so we can say they use a feature of that blockchain to create those tokens and deploy them and let them become tokens to be used as a medium of exchange. The fact that they do not have their own blockchain does not mean they cannot become a top crypto. It all depends on the acceptance and use by the crypto society.
These days there are many ICO and tokens but only few of them are legit. This is really a bad situation for overall digital currency.