The best open source alternative to Portmaster is NextDNS. If that doesn't suit you, our users have ranked more than 25 alternatives to Portmaster and many of them is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to 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.
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.
LuLu is the free, shared-source macOS firewall that aims to block unknown outgoing connections unless explicitly approved by the user.
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.
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.
Minimal Firewall is a portable Windows firewall frontend that alerts users to internet connections without requiring custom kernel modifications or disabling core isolation, striking a balance between TinyWall's security and SimpleWall's functionality.
Gufw is an easy, intuitive way to manage your Linux firewall. It supports common tasks such as allowing or blocking pre-configured, common p2p, or individual ports port(s), and many others! Gufw is powered by Uncomplicated Firewall (ufw).
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.
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AdGuard is great, but it's not a firewall/port system.