Google gives Android users a way to install unverified apps if they worked hard for it(including waiting 24 hours)
(android-developers.googleblog.com)
e/os and Sailfish are pretty popular alternative OSs (OSes? OSii?) and e/os is an android fork, with Sailfish having an android compatibility layer, so they work with standard Android apps.
Source: I use e/os.
Why are you in here arguing losing points with no reason or even knowledge about them?