Portmaster is described as 'Free and open-source tool that monitors all network activity, blocks unwanted connections, uses filter lists for ads and malware, enforces DNS-over-TLS, and sets custom app rules' and is a very popular Firewall in the security & privacy category. There are more than 25 alternatives to Portmaster for a variety of platforms, including Windows, Linux, Android, Mac and iPhone apps. The best Portmaster alternative is NextDNS, which is both free and Open Source. Other great apps like Portmaster are AdGuard, simplewall, Pi-hole and RethinkDNS.
NextDNS protects you from all kinds of security threats, blocks ads and trackers on websites and in apps and provides a safe and supervised Internet for kids — on all devices and on all networks.
Ad-blocking solution eliminating intrusive ads and preventing tracking, with malware protection. Filters pop-ups, banners, and more for clean browsing. Works in the background for ad-free surfing, protects data privacy with Spyware filter, and controls ad display in apps.
Simple tool to configure Windows Filtering Platform (WFP) which can configure network activity on your computer.
Blocks ads for all connected devices at the DNS layer without client setup. Provides web control, in-app ad and tracker blocking, DHCP and API support, regex filtering, privacy modes, audit logs, and long-term query analytics for network management.
Their is a comparison blog on safing.io suggesting when to use what solution https://safing.io/blog/2021/12/09/portmaster-vs-pi-hole/
An OpenSnitch-inspired firewall and network monitor + a pi-hole-inspired DNS over HTTPS client with blocklists.
Visualizes real-time and historical network activity, delivers alerts for suspicious behavior and unknown connections, manages firewall rules, reports DNS and system changes, identifies remote hosts, monitors app usage, supports remote monitoring, and detects possible threats.
Standalone firewall for Windows 7 and later featuring flexible rules by application, address, or protocol, wildcards, parent process filtering, SvcHost controls, blocklists, bandwidth graphs, traffic stats tracking, speed limits, and real-time network monitoring.
It's more lightweight than Portmaster. It notifies me every time a new app is in use even background programs. Plus it shows the file path for each app which makes it easier to make sure it isn't malware posing as legitmate software.
Firewall application for monitoring and controlling outbound network connections, notifying users of attempted access, supporting rule-based blocking, real-time alerts on suspicious activity, and preventing unauthorized data transmission on macOS systems.
InviZible Pro uses DNSCrypt Protocol, Tor and i2pd (I2P Daemon) (PurpleI2P) to achieve maximum security, privacy and comfortable use of the Internet.
Even though the firewall for this is less sophisticated, I still think it's a good alternative because of the dnscrypt protocol and anonymizing proxies. They're both "swiss-army knives" when it comes to privacy, but it's implemented in slightly different ways.
GNU/Linux firewall enabling interactive outbound network filtering, outbound application control, blocking of ads and malware domains, centralized GUI node management, input policy configuration, SIEM integration, real-time alerts, and user-level rule customization.
OpenSnitch is much more superior to any other software, especially astro-turfed Portmaster. Portmaster doesn't detect even a fraction of what is actually happening on your system, whereas OpenSnitch catches it all. It's an application firewall everyone should have! You'll be amazed how many stuff pretending-to-be-FOSS software is phoning home on you.
Comprehensive Windows software for internet traffic control, enabling users to set bandwidth limits for applications or connections. Offers real-time monitoring, long-term stats per app, and detailed internet usage reports. Ideal for managing data efficiently and enhancing network performance.
Free shared-source firewall for macOS blocking unknown outbound connections unless approved, alerts for unauthorized activity, helps detect malware, blocks OS or app data transmissions, no ads or tracking, audit-ready code on GitHub, enterprise event monitoring.
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AdGuard is great, but it's not a firewall/port system.