Aug 23, 2018 Little Snitch monitors outgoing connections, so the way it works is different than typical firewalls that are designed to block incoming connections. The free and shared-source alternative to Little Snitch that I know of is Lulu, from Objective Se.
Starting with macOS 10.15.4 the above “Legacy System Extension” message will be shown when Little Snitch is installed.
→ Please read this blog post to learn more about why this message is shown.
Will there be an update of Little Snitch that’s compatible with macOS 10.16?
Apps Similar To Little Snitch Full
Yes. We are going to release Little Snitch 5 later this year, which will be compatible with macOS 10.16. → Learn more…
Will I get the update for free?
Yes. All licenses sold now include a free upgrade to Little Snitch 5. In addition, customers who purchased Little Snitch 4 within a one-year period prior to the final release of Little Snitch 5 will also get a free upgrade. → Learn more…
Will Little Snitch 4 run on macOS 10.16?
Little Snitch 4 will not be loaded on macOS 10.16 by default, but there will still be an option to allow the loading. → Learn more…