Stocks, bonds, 401(k)s, annuities, etc. are great ways to earn passive income. If you're not financially savvy, you'll want to hire a financial advisor who'll help you choose the right investments for you. You may want to take a couple of finance classes to understand what your advisor is speaking about when he/she recommends an investment strategy. Done right, investments can pay off for years.
Buy a small business: A local small business, like a car wash or a laundromat, is a great way to put money down on a money-making venture. Automate it so you don't have to be on the premises unless you're collecting money. Go into a local business with your eyes wide open - study the books, especially on income and expenses, and examine water and utility bills if your venture will be open 24 hours.
* I use Personal Capital to track all my finances in one place. It’s much easier to use their free software to follow 28 accounts on one platform than to log into various accounts to check my balances. They’ve also got great tools for x-raying your portfolio for excessive fees, recommending a more optimized asset allocation, and planning for retirement with their Retirement Planner.