Y Combinator applicants listed Google and Facebook as their top competitors in 2016. Uber and Airbnb were gaining mentions as competitors, with Uber mentioned in 2.6% of applications. Slack messaging app has seen increased mentions as a competitor as well. For startups, being acquired by Google or Facebook is a major concern, as they worry about losing business to these large tech giants. The rise of subscription-based software-as-a-service models has also increased concerns for startups applying to Y Combinator.