Cheetah is a cross-platform, stand-alone sequence image player. I have developed it in C++ and embedded Python interpreter which allows us to reach and use the features of the application via writing Python scripts.
The application also allows us to paint directly on the GUI for taking notes for reviewing purposes. Those paintings can also be imported directly into Maya scenes so animators can use those review notes in the scenes they are working on without launching the application.
I have developed custom widgets for the application, like the time slider which indicates keyframes for painted frames.
Please do not hesitate to contact me for any reason at all.