A better description may be available at CurseForge
It's a clientside mod that attempts to improve overall satisfaction of the game through the introduction of various camera rotations, to emphasize on the player's movement and improve visual feedback. Strafing and turning around will tilt the camera sideways. Jumping, falling, and moving forward/backwards will affect the camera's pitch.
Currently, this mod is only available for Fabric. Any java developer is welcome to do a pull request with a port to Forge. I tried to make the code as less dependent on Fabric as possible.
You can find the configuration file with intensity scaling for all features at .minecraft/config/cameraoverhaul.json. Set a factor to 0.0 to turn the feature off. You can also use negative numbers there, if that's your thing.