Portmaster is a free and open-source privacy suite that puts you back in charge of your computer.

An OpenSnitch-inspired firewall and network monitor + a pi-hole-inspired DNS over HTTPS client with blocklists.

Visualize network activity in detail, get notified when new apps access the network, look out for malware, and block badly behaving apps.

A firewall protects your computer against unwanted guests from the Internet. But who protects your private data from being sent out? Little Snitch does!

LuLu is the free, shared-source macOS firewall that aims to block unknown outgoing connections unless explicitly approved by the user.

NetLimiter is an ultimate Internet traffic control and monitoring tool designed for Windows. You can use NetLimiter to set download/upload transfer rate limits for applications or even single connection and monitor their Internet traffic.

NetGuard provides simple and advanced ways to block access to the internet - no root required.

A powerful tool which extends the functionality of Windows Firewall and provides new extra features which makes Windows Firewall better.

OpenSnitch is a GNU/Linux application firewall.

Firewall (iptables frontend), based on DroidWall which is no longer being developed. A paid "donate"-version with more features it advertised within the app.

It lists activities, broadcast receivers, services, providers, permissions, signatures, shared libraries, etc. of any app

Ufw stands for Uncomplicated Firewall, and is program for managing a netfilter firewall. It provides a command line interface and aims to be uncomplicated and easy to use.