[$] Application monitoring with OpenSnitch

OpenSnitch is an
'interactive application firewall'. Like other firewalls, it uses a
series of rules to decide what network traffic should be permitted. Unlike
many other firewalls, though, OpenSnitch does not ask the user to create a list of rules
ahead of time. Instead, the list of rules can be built up
incrementally as applications make connections — and the user can peruse both
the rules that have built up over time, and statistics on the connections that
have been attempted.