Stupid Simple Solder Holder
As the name implies, this is an easy to print, easy to use solder spool holder. It will work best if you affix some sort of rubber on the bottom to provide grip, otherwise the whole thing might slide while pulling the solder from the spool. I used some adhesive-backed rubber sheeting from McMaster-Carr, which comes in handy for many such projects.
Print right-side up with no support. I used a 50% fill and that worked just fine. Add a rubber, non-slip bottom for best results.