One of the things I'm surprised your article doesn't mention is the tax advantages of this type of investment. The depreciation and rehab costs (purchasing distressed properties) can be huge deductions to ones income taxes, which none of the others have. Then, along with the appreciation of real estate, this passive income investment outperforms the notion of maxing out my 401k as well.
The first time I did affiliate marketing was way back in the day on my architecture exam website. I connected with a company that sold practice exams, which gave me $22 for every person who bought one of their exams via my site. Since then, I’ve generated over $250,000 simply by recommending that product alone. Again, this is a product that was not mine, but one that has still been helpful to my audience. This was all done with thousands of visitors a month. Not millions, or even hundreds of thousands.

Textile industry contributes about 4 per cent to the country's GDP, 14 per cent of the industrial production, and 17 per cent to export earnings.[189] India's textile industry has transformed in recent years from a declining sector to a rapidly developing one. After freeing the industry in 2004–2005 from a number of limitations, primarily financial, the government permitted massive investment inflows, both domestic and foreign. From 2004 to 2008, total investment into the textile sector increased by 27 billion dollars. Ludhiana produces 90% of woollens in India and is known as the Manchester of India. Tirupur has gained universal recognition as the leading source of hosiery, knitted garments, casual wear and sportswear. Expanding textile centres such as Ichalkaranji enjoy one of the highest per-capita incomes in the country.[190] India's cotton farms, fibre and textile industry provides employment to 45 million people in India,[189] including some child labour (1%). The sector is estimated to employ around 400,000 children under the age of 18.[191]
The first thing to do is figure out what you are good at and more importantly, what you enjoy doing. You may be able to type extremely fast. Maybe you have excellent negotiation skills. You may be great walking dogs and enjoy the needed exercise. Maybe you have a knack for growing gardens that homeowners in your neighbourhood covet. Tons of people are out there who do not possess the skills you have. You may have a needed skill that can generate a lucrative income in your spare time.
Putting your money into an established franchise business could also be a great source of passive income. Seeing that this type of investment offers a built-in process, wherein and they will mostly help you out in getting started and in its inner workings – even in finding a good location for your business. This allows you to have more free time as an owner.
In focusing on your wealth management goals, investment income is obviously critical but you might fund your goals from wider sources of income.  A typical long-term portfolio might produce about half its return as income and the other half as capital growth, though in times of duress the capital growth component wanes.  In this low-interest rate climate, some sources of income have become quite expensive and may prove disappointing against your spending needs.  But by tax efficiently and sustainably drawing income from wider sources, you might meet your goals while more prudently balancing risk against reward.