One of the main differences between Cal.com and Calendly is that Cal.com is an Open Startup. This means that we share all of our key metrics, and our source code can be accessed and contributed to via GitHub.
In addition, their pro plan is equal to our free plan for individuals, which contains all the essential features the average user needs. Settings and integrations that Calendly locks behind a paywall (monetization, analytics, etc.) are freely available to all Cal.com users.