There is only one file type that uses the .SPRITE3 extension:
Scratch 3.0 Sprite File
A SPRITE3 file contains graphics and animation information used by Scratch 3.0, an educational program used to develop creative programming skills. It is a Zip-compressed archive that stores a .JSON file, which includes information about the image as well as animation settings for the image.
Sprites are used by Scratch to perform actions within a project. Sprites can be created by users, but they are also available in the sprites library, as well.
To create a SPRITE3 file with Scratch 3.0, right-click the sprite thumbnail in the sprites panel, select, name the file, and choose the save location on your computer.
To open a SPRITE3 file with Scratch 3.0, clickunderneath the stage and select the SPRITE3 file on your computer.
NOTE: The release of Scratch 3.0 introduced the SPRITE3 file, which replaced the .SPRITE2 file used by Scratch 2.0.
Updated: February 24, 2020