Little Snitch 3.6 - Ah.

Name: Little Snitch
Version: 3.6
Mac Platform: Intel
Includes: K

OS version: 10.6 or higher

Whats new:

Little Snitch 3.6 is ready for OS X El Capitan.
Added support for watchOS and tvOS simulator apps.
Other improvements and bug fixes.

Courtesy of TNT Team

NB:

Please note, this a new variation on any previous K's etc on LS. There is a sn embedded in the .dmg which I know is technically against site rules but this app is a little special. By all accounts you can use any sn. Feedback would be appreciated as usual.

Do not update from this version.

Little Snitch... A firewall protects your computer against unwanted guests from the Internet. But who protects your private data from being sent out? Little Snitch does!
As soon as you're connected to the Internet, applications can potentially send whatever information they want to wherever they want.

Sometimes they do this for good reason, on your explicit request. But often they don't. Little Snitch allows you to intercept these unwanted connection attempts, and lets you decide how to proceed.

Little Snitch informs you whenever a program attempts to establish an outgoing Internet connection. You can then choose to allow or deny this connection, or define a rule how to handle similar, future connection attempts. This reliably prevents private data from being sent out without your knowledge. Little Snitch runs inconspicuously in the background and it can also detect network related activity of viruses, trojans and other malware.

More info: http://www.obdev.at/products/littlesnitch/index.html