In the very first episode, Edward Kmett talks about lens and a few of his other libraries. Then, near the end, he is asked about interesting Haskell stuff aside from his libraries. His answer, at 59:45:
"There was a really cool Commutativity monad [...] that really struck me as an interesting approach to things, I thought it was particularly neat toy."
— Edward Kmett
Yay, that's my library! And here are Wren's blog posts he mentions, about generalizing my approach.