Staking coin, these days there are a lot of altcoins which can be use as a staking and we get a reward of it. Although you must have a certain amount of coin to allow you being a staker. It mean you need to spend money first and a computer as service for staking coin.

Also affiliate marketing can be used as well to earn money even can be made as source income. As long as you have a lot of relation to many people then you can use it as an income. As an example an affiliate marketing for an exchange, you can share you refferal link to some people and you will earn money everytime he make a deposit/withdraw.