Keeping tabs on interesting software can be a pain, sometimes. But here goes:
Mac OS X Stuff
Real Wi-Fi Hacking
This guy (who is being Slashdotted even as I type this) has built a mini Linux distribution for the latest Linksys 802.11g router/access point. It's essentially a bunch of extra utilities to run atop the existing kernel, and installs on its RAM disk. Now that's some really interesting stuff.