Some well-funded startups have an unusual pitch for homeowners strapped for cash: Let’s own this house together.

A handful of companies, including those backed by marquee Silicon Valley names such as Andreessen Horowitz and Mark Zuckerberg’s philanthropic organization, are experimenting with a product that essentially lets them take an ownership position in a house along with the homeowner. The agreements, called shared-equity contracts, provide a new way for investors to get exposure to rising home prices across the U.S.

Shared-equity products are aimed at new buyers who need help with a down payment, or current homeowners looking for an alternative to a cash-out mortgage refinancing or a home-equity loan. The first use has caught the attention of mortgage-finance giant Freddie Mac , which recently agreed to buy loans on properties where one firm, Unison Agreement Corp., contributes to the down payment.

In those cases, home buyers get money for part of their down payment in exchange for pledging some of the home’s future price appreciation. The firms market them as a better alternative to low-down-payment loans, since they can give consumers more buying power without requiring them to take out pricey mortgage insurance.

Landed Inc. offers these down-payment contracts to teachers and other educators. Last year, the Chan Zuckerberg Initiative , a philanthropy co-founded by Facebook Inc.’s chief executive, gave Landed $5 million to start a new fund.