For many years there was no decent application firewall software for Linux.

Since a few years OpenSnitch has been packaged for a few Linux distributions.

Is OpenSnitch for you ?

Maybe not actually, it can be quite annoying having to choose what to allow and what not after a reboot of your computer if you are using more than just a few applications that need network access.

Why would you use it ? If you like to have more control about outgoing network connections from applications on your Linux desktop.

Do I like it ? Yes.

What did I learn with it ? Not much, but I remember wanting to saving html content from a newspaper site in LibreOffice for a friend (Usually I skip photos and want only text when I save an article for myself to read again later) and OpenSnitch came with a pop-up question because LibreOffice tried to connect to the newspaper site to fetch some missing images (or fonts ?).

Correction : Apologies. My memory was wrong. It was LibreOffice itself that asked to download missing remote content.

This information (That LibreOffice wants to fetch things) is not completely unimportant to me because I use VPN or Tor browser or i2p or Tor by other means or just plain Internet, and when I use the latter I prefer to only do this for a limited amount of sites.

More on OpenSnitch, Key Features, OpenSnitch in action (video) and more,

see here : https://github.com/evilsocket/opensnitch