François Quesnay further developed these concepts, and was the first to visualize these interactions over time in the so-called Tableau économique.[3] Quesnay believed that trade and industry were not sources of wealth, and instead in his 1758 book Tableau économique (Economic Table) argued that agricultural surpluses, by flowing through the economy in the form of rent, wages, and purchases were the real economic movers, for two reasons.
​Network marketing, or multi-level marketing, seems to be on the rise. Companies such as Young Living Oils, Avon, Pampered Chef, and AdvoCare are all multi-level marketing companies. You can earn passive income through network marketing by building a team underneath you (often referred to as a down line.) Once you have a large team you can earn commissions off of their sales without having to do much.
Purchasing a rental property is another common way that individual generate an income stream.  It is very similar to investing, in that you take a sum of money to purchase the property, and the property returns a cash flow – rent.  You do have expenses related to this that are different from investing, such as a mortgage, utilities, property taxes, etc, which all must be taken into consideration when calculating a return on rental property.
I would throw in some caution here: if your spouse works at the same company, or in the same industry as you, you are not diversified, and should something happen, you could be in a world of hurt.  Companies do go out of business, companies do lay employees off.  There is nothing wrong with working together, but realize that you are not diversified and you should be trying to maximize other income streams as a result.

In equity valuation, residual income represents an economic earnings stream and valuation method for estimating the intrinsic value of a company's common stock. The residual income valuation model values a company as the sum of book value and the present value of expected future residual income. Residual income attempts to measure economic profit, which is the profit remaining after the deduction of opportunity costs for all sources of capital.