The short-term real estate marketplace continues to flourish, raising another $850 million in new financing, according to a July 28 filing in Delaware. The new round of funding values Airbnb at around $30 billion. That's up $5 billion from just over a year ago. Airbnb, founded in 2008, remains among the top four most valuable privately-held companies in the world, behind Uber, Xiaomi and Didi Chuxing.