Some good writing here! I am a realtor myself and frequently get in touch with clients that consider buying a realty estate a conservative of investing. I once heard of a transport company in Vienna, Austria, which focused their entire profit on buying eventually every house available in the downtown for about 80 years. That must be some of a passive income!
Education is one sector which is totally immune from recession. I wrote an article on education sector Education – Problem or Solution There are many opportunities in education sector to earn Second Income. You can work part time or during weekends. Like foreign countries, in India also there is a demand for online tutors. You can earn handsomely as an online Tutor.
Portfolio income can come from multiple sources – interest/bond coupons, stock dividends, financial strategies including derivatives and capital growth.  Each offers some cash flow and some also offer potential capital gain with some risk from liquidity and volatile prices.  In this low-yield environment, many investors rely too heavily on cash flows and to pursue this are venturing further into riskier areas than they’d normally consider.