I've always thought that mold is the fungus, and to mould is to shape. When talking about it with my colleagues yesterday, I was surprised that this isn't common. Most people use one of the two spellings to refer to both.
Doing a quick search on duckduckgo also confirms that:
I'm not looking for what's correct or incorrect anymore, I just find it very fascinating that there are some people who use the words similarly to me, but the vast majority of others who use it in a different way.
So: what's the difference between mould and mold according to you?
I use mold for everything, but don't really bat an eye at using mould for the tool that is used to make parts which I see pretty often through my work.