That's: https://lede-project.org or:“Linux Embedded Development Environment” - the new project born from OpenWRT. I've used it with some old d-link routers, and I'm quite happy.

The documentation is still not stellar, but it has gotten better, and the configuration more consistent. It's quite easy to set up ssh-access with a key, and simply get a copy of configuration files with scp - ready to set up identical configurations on new router installs.