Gimp.app is a self contained application bundle of the GNU Image Manipulation Program for Mac OS X. It requires Apple's X11. Gimp.app is droppable, uses the gimp.print package built into OS X, and uses the system's default web browser for help and web browsing requests.
Actually Cinepaint was used for a quite a while in the movies where it served it's purpose rather well. There was a point in time where studios I believe were funding the development of it because commercial offerings at the time were poor. The list of movies is listed on the Cinepaint wikipedia page, and I'm not sure that's all of them. It seems like the last movie listed was back in 2003. As to why it's not more popular?
![Gimp 2.9 for windows 10 Gimp 2.9 for windows 10](https://imag.malavida.com/mvimgbig/download-fs/gimp-11185-2.jpg)
I'm guessing because studios switched over to commercial offering once Adobe and other software houses got their act together, and provided software with more features and support than Cinepaint. Photoshop seems to have had high bit depth editing for at least the last decade, and possibly longer.
Jul 06, 2017 How to Download and Install Gimp for Macbook Air / Macbook Pro / Mac. How to Use GIMP 2.10 Basics Beginners Guide. 10 macOS Tips for New Mac Users - Duration: 9:16. 9to5Mac 480,499 views.