It's an interesting alternative to Gecko, KHTML and WebKit and a semi-alternative to Chromium (though based, like Chromium on Blink)
Qt WebEngine integrates Chromium's fast moving web capabilities into Qt.
Our goal is to bring the latest and best implementation of the web platform into the universe of Qt. The integration with Qt focuses on an API that is easy to use, yet extensible. We also make no compromise on the graphics integration, integrating the layer rendering of Chromium directly into the OpenGL scene graph of Qt Quick.
Relationship to Chromium
Qt WebEngine uses code from the Chromium project. However, it is not containing all of Chrome/Chromium:
Binary files are stripped out
Auxiliary services that talk to Google platforms are stripped out
The codebase is modularized to allow use of system libraries like OpenSSL
We do update to the latest Chromium version in use before a Qt release. After a release some bug fixes and security patches are backported. For LTS releases of Qt we might also update Chromium in a patch level release.
Wikipedia article on web browsers and what they are based on: