Technically speaking, it is illegal to develop an app similar to others with paid free features in the original app. It's like making a clone.

APKMB. Website //apkmb/ ...

Mobilism. Website //forum.mobilism/index.php. ...

APK4ALL. Website http://apk4all. ...

Android Hackers. Website androidhackers.io. ...

APKPure. Website m.apkpure. ...

APKCombo. Website http://apkcombo/ ...

Reddit. Website //reddit/r/ApksApps/ ...

HappyMod.