Wifi Automation is a program that can automatically perform actions (launching programs, killing programs, adjusting system volume) based on connections to and disconnections from wifi networks. It works with Windows Vista and Windows 7, and if you're lucky, XP SP3.
I use it to automatically start Synergy when connected to my own wireless network and stop it when disconnected. I also use it automatically mute the volume when I'm connected to my school's network, since I don't want any sounds playing during class, and turning it back up when I'm connected to my own network.
See the help file for more information on how to use Wifi Automation.
Version 1.0 is the current version.
The source code is located here.