Twitter emoji (discord uses these also) are open source: https://twemoji.twitter.com/
Both of these are very consistent and good open source emoji. I think in the past a lot of these projects that were not backed by companies eventually devolved into a paid product that was no longer open source, but I'm hopeful that openmoji continues down the FOSS path.
[0] https://dn-works.com/ufas/
[1] https://web.archive.org/web/20180129230141/http://users.teil...
[2] https://web.archive.org/web/20180302032711/http://users.teil...
Namely these (paraphrased) snippets:
1) The developer retains all rights to previous, current and future versions of UFAS.
2) Users are prohibited from network installation.
3) Users are prohibited from redistributing UFAS.
Developer can't retains rights granted with previous versions of "Symbola".
> NotoColorEmoji uses the CBDT/CBLC color font format, which is supported by Android and Chrome/Chromium OS. Windows supports it starting with Windows 10 Anniversary Update in Chrome and Edge. On macOS, only Chrome supports it, while on Linux it will support it with some fontconfig tweaking, see issue #36. Currently we do not build other color font formats.
[0]: https://openmoji.org/library/#group=extras-openmoji%2Fclimat...