Freshmeat page: http://freshmeat.net/projects/beep/
beep does what you'd expect: it beeps. But unlike printf("\a"), beep allows you to control pitch, duration, repetitions, etc. Its job is to live inside shell/perl scripts and allow more granularity than one has otherwise. It is controlled completely through command line options. It's not supposed to be complex, and it isn't - but it makes system monitoring (or whatever else it gets hacked onto) that much more informative.
To date, I've heard of beep specifically being used:
This project has the following developers:
New HTML Parser: The long-awaited libxml2 based HTML parser code is live. It needs further work but already handles most markup better than the original parser.
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If you're a C programmer with some spare time, take a look at the mod_virgule project page and help us with one of the tasks on the ToDo list!