DewDrop Studios (http://www.dewdropstudios.net) has launched NetUse Traffic Monitor 1.0 for Mac OS X (10.6.6 and higher). It costs US$4.99 and is available at the Mac App Store in the Utilities category.
NetUse provides a way to monitor your network traffic on the Mac. Utilizing the SNMP feature of any modern Internet router or gateway, the software monitors and collects real-time Internet usage statistics for all the computers in your home or office that share an Internet connection.
If you have a traffic cap on your Internet usage, NetUse will help to make sure you don’t exceed your limits, says Andrei Grichine, founder of DewDrop Studios. Set your billing date and a monthly traffic allowance and NetUse will accurately show how much bandwidth you consume, he adds.