.aecache viewer, it can view any raw bitmap image, but I made this for the specific purpose of opening .aecache files from the Disk Cache folder. Useful in an obscure event of a total backup failure of project files, and recovering rendered cached frames makes sense. Or if you are curious how AE stores cached frames, or maybe for cherry picking which cached frame to purge.
Can read metadata that was made by After Effects, if there is no metadata in the image the feature for guessing dimensions based on the file size should help.