Free-to-use Cash Earning
If cryptocurrency isn't your thing, check here for ways to earn some good old US dollars for free. These methods are usually very slow, but they do work if you put the time in (much less passive than other income opportunities).
Get paid to share your unused internet connection
Download, install, create account and let Honeygain provide truly passive income for you by sharing your spare internet connection. Especially useful for people with unlimited internet/mobile data plans. 1GB used by Honeygain = 100 credits. 1000 credits = $1USD. Users need to reach $20 to withdraw. "Content delivery" can be enabled for additional earning potential, but I am still queued for this service so I don't know exactly how it works.
InboxDollars (Proven Passive Stamped)
Longstanding, trusted earning platform with many ways to earn
InboxDollars has it all: surveys, paid emails, games, coupons, a browser extension, paid search bar...just a ton of ways to earn money doing things you already do. Once you reach $35, you can cash out. Now, it's been many years since I actively used InboxDollars and the last time I cashed out they sent a paper check in the mail, but they have since added PayPal support.