Installation:
$ pip3 install LUASprites
Usage:
$ luasprite spritefolder
Where spritefolder is the directory containing the images you want combined on the sprite sheet
The spritesheet will be stored in a new directory named output(number) parented to the spritefolder given as a command line argument. For more information regarding this tool, please refer to the Roblox documentation: [DEVFORUM LINK HERE]