Maybe you’re obsessed with homemade jewelry and want to sell your wares on Etsy. Or, perhaps you’re well-versed on the Amazon reselling game and want to earn extra cash finding unicorns (rare and valuable products) and reselling them for profit. Maybe you’re obsessed with a specific topic and want to start a blog that can one day bring in advertorial and affiliate income.

I’m on board with having more than one source of income, but I definitely want to make my “extra” income as passive as possible. I don’t want to end up pushing myself to always earn more, more, more and never enjoy the life I have. Having said that, it’s nice to have the security blanket. My blog doesn’t earn much, but I also know it could earn more if I really needed it to. It also helps to l

1) If your property is not under rent control, you have the ability to raise rent to market prices with proper warning. In SF, I have to give tenants a one month warning for up to a 10% increase and a two month warning for up to 60%. Rent control limits to an inflation index, usually around 2% a year, which is why initial pricing and tenant turnover is important for better profitability.
However, until we get another reset in valuations (I’m calculating a 40% to 50% correction is justified ), I’ve moved largely to the sidelines. Beginning in July 2013, I began slowly reducing equity exposure and am now sitting firm at 40% with the balance in various forms of 5 yr cd’s and short duration bonds. This is down from over 60% when I ramped up to take advantage of the March 2009 lows.
Nobody gets early FI investing in bonds, CD’s, or even stocks unless they make a huge income or are extremely frugal or a combination of both. Paper assets just don’t provide enough returns. Business income can be great but it is typically not as semi-passive as I would like and there is a relatively high failure rate. That is if you can monetize an ideal to begin with. RE investing needs to be higher ranked IMO as a way that the “average guy” can become FI.
Basically, people looking to borrow money will make a listing on the site. Those borrowers are then placed into a category and given a “rating” based on their credit history and rate. You, as an investor, will contribute money to these loans and then be paid back at the predetermined rate of interest. Invest and see those monthly interest payments deposited into your account.
The other point is that it is pretty easy to get started.  You don’t need to be super rich, and you don’t need a lot of time to get started.  To say it requires no time would be a lie, but you don’t need to make anything listed above your life.  You can work at your job, invest your excess income, save to buy a rental property or rent out a room in your current house, and you start a side job online without breaking a sweat.
What I’m doing: My realistic goal is to have a blended annual return of 2x the risk free rate. With a current 5% hurdle, I am not paying down mortgages that cost less than 4%. Debt at 5% is a wash. My realistic blue sky scenario is a 3-4X rate of return over the risk free rate which can be achieved with property, stocks so far for the past five years, and certain private equity investments. Where I am dragging is my blended average CD interest rate of roughly 3% from an old CD coming due. I’ve rolled some money into a 12-month CD with CIT Bank at 2.5%. It’s the best rate I can find. 
There are a ton of ways to diversify your investments, some of which can send real income your way. By opening a brokerage account and investing in ETFs or mutual funds, you can earn real returns you can use to supplement your income. Of course, the flip side can also happen – as in, you can lose money. So, make sure you understand the risks before you dive in.