Wifi Protector is an app that reports if your WiFi connection is being hijacked, sniffed, or blocked. Additionally, if you're a rooted user, it can prevent you from being shut down via WiFiKill.
In non-root mode, it works by monitoring network-related information, and when abnormal routing data is received it will alert you that your connection is being tampered with, WiFikilled, etc. In root mode, it's possible to make your EVO refuse to fall for the methods used to re-route data and thus maintain a connection.
While the uses for this are fairly slim for most of us, if you find your internet connection randomly going out whenever someone is around it's a useful tool for seeing if they're booting you off. Or if you're worried about using public WiFi, you can at least probably rest assured that all your unencrypted traffic isn't being sniffed by the random person who just showed up at the coffee house and laughs from across the room every time you visit a new page on icanhazcheeseburger.com.
Wifi Protector is $1.32 in the Android Market, but you can drop by the development thread and try it out before you buy it.