What is this?

An unofficial overlay obviously, to experiment with ebuilds.

To manually add overlay:

layman -f -a gentoo-overlay-trent -o https://raw.githubusercontent.com/TrentSPalmer/gentoo-overlay-trent/master/overlay.xml 

Test drive?

Here's a Gist with instructions for how to quickly spin up an nspawn container to do some test building, if you are into that sort of thing.