I'm already familiar with coinbase and Gdax but they only cover four coins at the moment.
What is a good exchange where I could buy and sell alt coins like Ripple, Dash, Monero, and Cardano?
Ideally, the fees will be zero or very low. Obviously I want something secure as well.
Why not trade directly on an exchange? Binance is a good exchange, you can trade here, you should master this skill.