title: What is a kind projector
body: <p>I've been digging into FP and everything that surrounds it, and I found the concept of kind projector written somewhere, without details nor explanations.</p>
  
  <p>The only thing I found was this <a href="https://github.com/non/kind-projector" rel="nofollow">github project</a>, and I'm starting to think if it was referring to this particular project, or to some generic concept in FP?</p>
  
  <p>So, what is a kind projector? Why is it useful? (if possible, can you provide examples, resources, etc?) </p>