According to the Cocoa Packet Analyzer website:
Cocoa Packet Analyzer is a native Mac OS X implementation of a network protocol analyzer and packet sniffer. CPA supports the industry-standard PCAP packet capture format for reading, capturing and writing packet trace files.
Features:
- Basic packet capturing (libPCAP/ tcpdump filter expressions can be used).
- Analyze, display and filter packet trace files.
- Supports PCAP packet capture format.
- Quicklook plugin included – it is basic but at least you can get an overview over packet trace files in finder.
- Intel 64-bit CPU support.

Cocoa Packet Analyzer screenshot
Software
free, OSX, packet sniffer
Synthesia is a very cool game for beginner, novice and expert piano players. At first sight it looks a little bit like Guitar Hero, but now it is used for piano. Here are some more screenshots. Nice about synthesia is that it is free. The free version can load all the midi files you want, but does not show any sheet music. If you want to see the sheet music you have to buy Synthesia for $18.

Synthesia screenshot
Software
free, music, piano, Software
Some love it, some hate it: Flash based document browsers. Instead of downloading a pdf, your visitors can literally browse through the pages. Flashpageflip.com offers a free version of thier FlashPageFlip tool. Here are some examples of FlashPageFlip in action.

web
flash, free
Battlefield heroes is a free cartoony first person shooter. From the Battlefield heroes site:
- Battlefield Heroes™ is a free cartoon-style shooter for the PC
- Combining classic gameplay with brand new innovations, it’s a totally new experience
- Cartoon-style graphics bring the fun back to shooters
- Third person camera so your Hero is centre-stage!
- Create your own unique war Hero with extensive character customisation system
- MMO-like special abilities add strategic depth to combat
Make sure to checkout the screenshots on the Battlefield heroes website.

Battlefield heroes logo
Software
free, games, windows