I personally use EagleFiler to organize stock icons and other assets that I’ve purchased. I have them arranged in folders based on how they were bought, with smart folders to find different types of files and tags to keep track of which projects I’ve used (or considered using) them in.
I have another library to checksum my “finished” Lightroom photos.
Would be interested to know what others are doing and if there are any additional features that would help for this type of use.