Blender's success is a lot due to how welcoming they are of new contributors.
15 years years back, this was the first big OSS project that I contributed to. Since I was a greenhorn, the patch I submitted (there weren't 'PR's back then :) ) was, to say the least, rather shoddy.
Ton Roosendaal helped me patiently on the IRC (I think they were on Freenode back then, not fully sure), guiding me through the changes needed to make it acceptable to merge it.
I learnt a ton just hanging out in the dev channel. Good times. It was a great product even back then but it's amazing how much more awesome it has gotten since then.
Great work Blender team.