ViperOS is described as 'The Viper Project is a Brazilian Open Source Team Project. We believe in Dreams Come True'. There are eight alternatives to ViperOS for Android, Android Tablet, Android Wear and Linux. The best alternative is Android, which is both free and Open Source. Other great apps like ViperOS are LineageOS (Free, Open Source), /e/ (Free, Open Source), CalyxOS (Free, Open Source) and LineageOS for microG (Free, Open Source).
A free and open-source operating system for smartphones and tablet computers, based on the Android mobile platform. It is the successor to the highly popular custom ROM CyanogenMod, from which it was forked in December 2016 when Cyanogen Inc.
/e/ is a fork of LineageOS that aims to be completely free of everything Google. Not only that, but there are a number of goals the developer has in mind for /e/ that more people feel are vital to a mobile operating system.
Everyone needs a phone. Not everyone wants governments and corporations tracking their every move and spying on their communications. CalyxOS lets you have your cake and eat it too, with "Privacy by Design".