Bandwidth shaper or bandwidth controller application for Mac OS X I'm looking for a bandwidth/packet throttle/shaper program with the following features:


Similar to Windows-based Netlimiter.
GUI based and not terminal or command line.
Shows list of all applications communicating over network its connections, transfer rates and more.
Set download or upload transfer rate limits for applications, connections or groups of them.
For those on 10.7 or newer, the easiest solution to the bandwidth limiting part of the question is Apple's Network Link Conditioner (NLC), a free utility that was originally included with Xcode. Then Apple got all sandbox-happy, so now it's a separate download from Apple's developer web site, called the Hardware IO Tools for Xcode.
The important points going for NLC are that it's from Apple, it's got a very straightforward UI, and it works. Some of the other suggestions given in other answers fail some or all of these criteria, particularly in failing to work on newer OSes.
As for monitoring per-application bandwidth usage, I recommend iStat Menus.