okay this is super fucking excellent:

https://obdev.at/products/littlesnitch-linux/index.html

thank you @cR0w for letting me know it exists.

little snitch is fucking awesome. its the de-facto host-level firewall for macs these days and its impressively effective.

to have this for linux?

game changer.

Little Snitch for Linux

Discover powerful applications such as Little Snitch Mini, Little Snitch, LaunchBar and Micro Snitch.

Objective Development
GitHub - evilsocket/opensnitch: OpenSnitch is a GNU/Linux interactive application firewall inspired by Little Snitch.

OpenSnitch is a GNU/Linux interactive application firewall inspired by Little Snitch. - evilsocket/opensnitch

GitHub
@quikkie @Viss I tried that one myself and I like the idea but it was always more of a hassle to manage than I was willing to deal with.
@cR0w @Viss rough edges? Yeah, later versions are better but not littlesnitch great.