Which real estate marketplace startup was co-founded by Rich Barton and Lloyd Frink? Zillow.
Barton and Frink, both veterans of Microsoft and Expedia, began developing Zillow in the mid-2000s. Barton had already helped create Expedia and saw an opportunity to bring similar consumer-friendly transparency to real estate: buyers wanted photos, listings, sale histories, and a straightforward estimate of what a home might be worth.
Zillow was incorporated in Washington in December 2004 and launched its website on February 8, 2006. Its early signature feature was a free home-value estimate, later branded as the “Zestimate.” The site attracted so much attention on launch day that its servers reportedly crashed under the traffic.
The question identifies Barton and Frink as co-founders, which is the standard concise answer, though Zillow's broader founding team also included Spencer Rascoff, David Beitel, and Kristin Acker. StreetEasy and Trulia are not alternate founding answers: Zillow later acquired StreetEasy and bought Trulia in 2015.