Robinhood's publicly reported system is a pre-launch viral architecture layered on a commission-free trading product. The components are publicly documented across multiple referral-marketing analyses and Robinhood's own pre-launch marketing materials.
The pre-launch waitlist was the load-bearing structural primitive. Each prospective user who signed up received a queue position; the queue position was advanceable via referral activity. A prospective user could climb the queue by sharing their referral link with others who then joined. The publicly described mechanism was that queue-position-as-reward and free-stock-on-launch (randomized $5-$200 lottery dynamic) compounded into a single incentive that motivated referrals at scale.
The post-launch member-referral free-stock program continued the same architecture in steady state. Existing members invite new members; both receive a randomized free stock (publicly reported between approximately $5 and $200 in value); the social-shareability of the random stock value (members publicly posting their results on social media) extended the viral loop into organic social channels.
The product itself — mobile-first, commission-free trading with no account minimum — is the publicly described structural enabler. Without commission-free trading, the long-tail retail audience the referral loop acquired would not have converted to active accounts; the publicly described product economics work because the referral loop acquired members the unit economics of commission-based brokerages could not have economically served.