Free & Open-Source ZoneAlarm Extreme Alternatives

Personal firewall and antivirus.

1. Microsoft Defender ↗
   Built-in Windows antivirus — solid baseline.
   ●●○Medium · Different UI, similar features
2. OpenSnitch ↗ FOSSPRIVATE
   GUI application firewall for Linux.
   ●●○Medium · Different UI, similar features
3. Portmaster ↗ FOSSPRIVATE
   Privacy firewall for Windows + Linux.
   ●●○Medium · Different UI, similar features