Thanks! I chose it because I want it to be public domain, people can copy, remake, improve, do whatever they want with it. Don't having to worry about any infringements.
I've opened up the repo now (https://github.com/CoreyGinnivan/system-uicons), the licence is officially "Unlicense License" - it's all public domain. The SVGs are all in the repo (or can download on the site). I'll be releasing Sketch and Figma files soon :)
This project actually started because of that haha. I've started off with a mix of obscure and commonly used icons, but I've got another 200 coming soon, and will continue to make more.
I'm also setting up the site with a request option. Just wanted to get the project out otherwise it'd never get out :)
Is there anything that you're currently after? Will try and sneak it in to the next release.