I rent out two single family homes. You need to learn about how to analyze your return on investment, get the places rented, and deal with repairs, problem tenants, among other things. If you don’t do your research, you could easily lose money. I have to spend a few days a year managing things, checking up on the properties, finding new tenants, but it is effectively passive. I buy in areas near big universities with stable real estate markets so there is always a fresh crop of new people moving into the neighborhood.
If you're looking to get started in real estate, look at a crowd funding solution like RealtyMogul. It works similar to LendingClub - you commit as little as $5,000 towards a property. When the property is fully funded, you become an owner, and will receive your share of the earnings and appreciation in the property.  Check out RealtyMogul to learn more. 
Truebill is an app that helps you save money by identifying recurring subscriptions and other bills and helping you cut costs by negotiating better rates and fees. One of their partnerships is with Acradia Power, which has the potential to save you up to 30% on your electric bill. It searches for better power rates in areas where competition is allowed, and it locks in the better prices for you.

There is also an idea that we should work to build a passive income asset and then sit on the beach relaxing for the rest of our lives. The truth is that most people would get extremely bored with this scenario and will be eager to find something to do. That’s why the world’s billionaires continue to work… they love what they do and it stopped being about the money a long time ago.