It's FOSS - https://itsfoss.com/eelo-mobile-os/
Brief: eelo is a new mobile OS based on open source Android distribution LineageOS. Its creator is trying to build an ecosystem which is free from Google and Google related products.
After the demise of Ubuntu Phone and Firefox OS, there are not a lot of open source mobile operating systems left in the market. But this doesn’t discourage people from trying something new in this not-so-successful domain.
A couple of months we saw the announcement of ultra-secure and privacy-oriented Librem Phone. And now we have a new crowdfunding campaign for a new open source mobile operating system called eelo.