I saw a poster on TIGSource talk about manually cutting up sprite sheets, so I’ve dusted off a project from 2007 to solve it. Just load up a sprite sheet, select the background color, and export the results into a directory. It’s got a few extra features useful for what I originally wanted it for, too.
Just remember, this is from the archive, so way crappier than the stuff I do nowadays. I’ve barely touched it, except to brush off a few GUI bugs and delete menu options that don’t do anything.
But it does the job.