LuLu is the free, shared-source firewall for macOS. It's goal is simple; block any unknown outgoing connections, until approved by the user. While it was designed to generically detect malware by flagging unauthorized networking connections, LuLu can also be used to block OS components or 3rd-party applications from transmitting information to remote servers.

Little Snitch is a trustworthy and handy macOS application capable to monitor your network traffic and block various connections in order to protect your privacy.

Murus Pro unleashes the great power of PF, offering a very wide set of features. It is a complete frontend for PF, and is bundled with Murus Logs Visualizer, an app to analyze PF logs and statistics, and Vallum, an application-layer firewall with real-time notifications. Access all advanced options to build and maintain a fully customized network infrastructure with your Mac.

Radio Silence is an outbound application firewall that lets you block Internet access from individual apps.

The Firewall – Network Monitor application gives you the full control over your Mac, protects the privacy of your computer, prevents unwanted network connections. Full Network Transparency!

Protect your privacy. Keep an eye on Internet connections from all applications as to expose the hidden connections. Prevent them from sending data without your consent, hence avoiding information leakage.

Little Snitch 4 gives you control over your private outgoing data.

Track background activity 
As soon as your computer connects to the Internet, applications often have permission to send any information wherever they need to. Little Snitch takes note of this activity and allows you to decide for yourself what happens with this data.

Scudo is a hybrid firewall for macOS that combines an inbound network-layer packet filter with an outbound application-layer firewall. Scudo helps protecting your Mac’s network services from unwanted connections from remote computers and improves your privacy and security controlling all apps network activities, allowing you to choose which app is allowed to connect to the network.

Vallum is a little tool that helps you monitor and block application connections. It is able to intercept connections at the application layer, and hold them while you decide whether to pass or block them. Vallum's interface is very simple and is icon-based. Its default configuration is not intrusive, and it does not require any interaction or specific networking knowledge or skills. Just drag an app's icon from the Finder into the main Vallum window to block it. To change Vallum's attitude and interaction level, you just have to play with the very few options available. Intercept apps that leak data on the network, drag apps' icons to create firewall rules, run the firewall with one mouse click: Vallum is friendly, it stays in a corner of your Mac's menu bar on top of the screen, it does not pollute your Dock and your desktop, it features a simple interface that everybody can use, and it's powerful because it lets you create complex setups with jails, mixed rules, notification pop-up alerts, and temporary rules, at both application- and network-level interacting with Murus and the macOS built-in PF packet filter.

TripMode automatically reduces your mobile data consumption when you use a mobile hotspot

Hands Off! is an application to monitor and control the access of applications to your network and disks. Being able to monitor the normally unnoticeable activities enables you to make informed decisions regarding the transfer of your private information, hence avoiding confidential information leakage.

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

This functional and easy to use tool for OS X platforms can be used to monitor the activity of applications that can establish a connection to the Internet. Thanks to Hands Off! user will be able to timely detect signs of malicious or potentially dangerous activities, to eliminate the possibility of leakage of confidential data and prevent malicious programs to a personal computer.

Murus Pro unleashes the great power of PF, offering a very wide set of features. It is the most complete front-end for PF. and is bundled with the companion app, Murus Logs Visualizer. Access all advanced options to build and maintain a fully customized network infrastructure with your Mac.