Few ways I have done it which is really passive (means not even managing anything)
- Hard Money Loans and Equity deals of Real Estate
- Other kind if diverse loan types again where someone else is managing the serving collection and legal work
- Getting land (since it doesn't require much management) and selling for profit or renting for agriculture
- Of course Investing in dividend stocks is the most common and most preferred day
- Investing in stocks along with conservative option writing strategies.
- CDs and bank interest - but currently its very low but just few years ago you could get 3% for 5 years
- investing in precious metals - it doesn't generate any income but can be sold for capital gains - look at a gold chart of 20 years!

Of course I might be missing multiple other ways that are possible.