Firewalls are great for blocking incoming traffic to protect your computer. However, I’ve always wanted to know in real-time whenever a program on my Mac attempted to establish an outgoing connection to the internet. Enter Little Snitch, the program does just that, it tracks the outgoing traffic. Some programs “phone home” to establish a presence such as chat clients while others do it to verify registration information. The program doesn’t get down to the TCP/UDP level but instead a high-level overview of where your programs are connecting to. After running the program for a couple days, I realized that Skype is one chatty program, I noticed it connecting to other Skype Supernodes every couple seconds. I also noticed that the Apple ntpd (network time protocol daemon) would access the internet every 4-5 minutes, presumably to update the internal clock. All other outgoing traffic was expected.
If you like to know what your programs are doing when connecting to the internet or like to watch your bandwidth then Little Snitch is great.