As a developer, this bears repeating:
“Free” does not mean a single thing
from a legal licensing perspective.
You have to include an explicit license with your “free” work, otherwise developers wouldn’t—or at least shouldn’t—touch it with a ten-foot pole.I have agonized over this when trying to find icons I could use for my open-source GitHub project, and it wasn’t easy. When I was looking into it, I compiled a short list of great icon sets and their respective licenses to wrap my head around whether I could use them in my project at all: http://pygm.us/QRelV0PW.
As a developer, I know how hard it is to figure out how to license your work, but licensing is one of those things we really, really need to understand and come to grips with.
And don’t get me started on contributor license agreements ...