GMS Explorer is a program to open, view, extract, and edit the contents of data.win files of Game Maker Studio games. This is intended to be a more full-featured successor to GMExtract.
A large portion of the information used to reverse-engineer the format is from PoroCYon here and Mirrawrs here. Big thanks to them for figuring out and sharing this much.
Can read in a file and browse through sprites. Also allows extraction of all of a sprite's frames.