New in Craft CMS 3.3
As always, I have linked the complete changelog for those who want to read all the details about the release.
GraphQL: Craft Pro has received an important innovation with the built-in GraphQL API. Define which content should be public and additional schemes requiring private tokens.
Headless Mode: The headless mode is probably the most significant new feature, which will please those who want to use Craft as a CMS for a single-page app or static site generator like Gatsby. In this mode, various URL fields in the control panel are removed, and the template settings no longer have any effect, as Craft is completely decoupled from the frontend.
Single entries without URL: It is now possible to use single entries/singles without an associated URL.
Better Twig profiling: Craft can now examine individual template blocks and macros instead of just complete templates. This should make it easier to find performance bottlenecks.