&gt; Impossible on OS X and Linux without shelling out $$$.<p>I&#x27;ve <i>never</i> used it, so I can&#x27;t endorse it, but this was among the first results in a google search for &quot;linux per application firewall&quot;:<p><a href="http:&#x2F;&#x2F;douaneapp.com&#x2F;" rel="nofollow">http:&#x2F;&#x2F;douaneapp.com&#x2F;</a><p>I guess there has been progress in this space since you last looked.<p>There is <i>also</i> SELinux controls that can be used... so -IIRC- you could create a per-app firewall with that. :) I would be <i>slightly</i> surprised if there weren&#x27;t pretty reasonable GUIs for managing such SELinux rules.