The best open source alternative to Little Snitch is Wireshark. If that doesn't suit you, our users have ranked more than 25 alternatives to Little Snitch and 19 is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to Little Snitch are Portmaster, LuLu by Objective-See, Fort Firewall and NetGuard.
Wireshark is a premier network protocol analyzer used globally in industries and education, offering multi-platform support, deep protocol inspection, powerful display filters, and VoIP analysis. It allows both live capture and offline analysis, supporting various networks and protocols.
Free, open-source privacy suite monitoring all network activity, blocking unwanted connections, using trusted filter lists for ads and malware, enforcing DNS-over-TLS, providing custom app and global rules, and supporting advanced privacy management.
LuLu is the free, shared-source macOS firewall that aims to block unknown outgoing connections unless explicitly approved by the user.
I've used Little Snitch for many years. However, after buying a new Mac I was faced with buying licences for a whole bunch of apps I had paid for several times in the past. Given this unwanted additional expense and the fact that I really don't need all the extra features of the later versions of Little Snitch, I decided to try alternatives. LuLu absolutely fits the bill for the purpose of stopping apps phoning home without your permission.
Free (Libre) Software is and will be always best for the humanity :)
NetGuard provides simple and advanced ways to block access to the internet - no root required.
InviZible Pro uses DNSCrypt Protocol, Tor and i2pd (I2P Daemon) (PurpleI2P) to achieve maximum security, privacy and comfortable use of the Internet.
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.
Lockdown Privacy is an Open Source and free firewall for your iOS device. We built the product to help protect users from app developers and analytics companies that are monetizing user data without consent or transparency.
A fundamental re-design of user Data Privacy. Your multi-tool for online protection. So easy your grandma could use it. Costs less than a cup of coffee per year.
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I Wanted a tool to replace Little Snitch, and this one is GREAT. It is Free, Open Source, and very lite weight.