Ploopy, famous for their open hardware trackball, recently released a new product, the Ploopy Headphones. I’m not much of an audiophile so cannot vouch for how good they are audio-wise, but it is very cool that you can make your own headphones from scratch, from amplifier and firmware, up to the custom 3D printed casing. Check out the Github for sources and an in-depth wiki howto.

https://ploopy.co/product-category/headphones/
https://github.com/ploopyco/headphones