Castle

Max Nussenzweig and his two co-founders identified a fundamental problem in the rental property management industry: traditional property managers charged percentage-based fees (averaging 10-13% when all fees were factored in) plus markups on maintenance work, creating perverse incentives for them to inflate costs and recommend unnecessary work. They saw an opportunity to build a transparent, flat-fee alternative that aligned incentives with property owners.

The team founded Castle in late 2014 and launched in Detroit in early 2015. They chose Detroit strategically—not because of the startup ecosystem, but because of the city's affordable real estate market with strong rental yields. A three-bedroom brick home could sell for $40,000 and rent for $800/month, making it accessible to regular investors. The founders built Castle as a hybrid SaaS-physical services model: they find tenants, collect rent, coordinate maintenance, and manage properties end-to-end for a simple $79/month per unit fee, regardless of rent amount.

By May 2016, Castle was managing 530 units across approximately 400 properties, mostly single-family homes and small multi-units in the Metro Detroit area. The business model proved especially appealing to small landlords underserved by traditional property management companies. With a 10-person team (9 in Detroit, 1 remote in LA), Castle achieved $31,000 in monthly recurring revenue. The average customer owned 2.2 units, translating to approximately $174 monthly revenue per customer.

The key insight was targeting the "regular person" real estate investor rather than institutional investors or funds. Traditional property managers' complexity and incentive misalignment drove high switching costs—customers often stayed with inferior services just because switching was painful. Castle's transparency and flat-fee model created a competitive advantage. The company maintained an impressive 1% monthly churn rate, losing customers primarily only when they sold properties. Max attributed this to high switching costs and customer satisfaction.

The team also thought strategically about customer acquisition, willing to spend ~$200 per unit acquired, which scaled proportionally with customer size. With an estimated 24-month customer lifetime (conservative due to limited operational history) and $174 average monthly revenue per customer, the lifetime value math worked: roughly $4,176 per customer supported their acquisition strategy.

As of May 2016, Castle had raised just under $3 million total, including a $2 million seed round on SAFEs (with a cap but no discount or interest) right after graduating from Y Combinator's Winter 2016 batch. The company was preparing to expand beyond Detroit into markets like Phoenix, Atlanta, Las Vegas, and South Florida—all affordable rental markets underserved by Silicon Valley-centric property tech companies. Max emphasized that the business tracked SaaS-like metrics (MRR, churn, LTV) despite the physical component, signaling founder sophistication about unit economics and growth.