It looks like you have found my personal portage overlay. This overlay contains mostly random ebuilds that may or may not be useful for somebody.
The overlay is available through app-eselect/eselect-repository. After installing, you can add it by running
eselect repository enable jm-overlay
Everything in this overlay should be considered experimental! While I try to write ebuilds with reasonable quality, they are mostly just tested on my personal machines (amd64). Since Gentoo can run in many other configurations, there might be cases where an ebuild won't build or install correctly. If that happens to you, please feel free to report the problem on Github so I can fix it.