Trial version has all the functionality of the registered version expect that it will not run one thenth of the configured applications.
Once launched, MacIfMon will monitor status of network connections on your Mac (both LAN and dial-up connections). If it detects status change on any of monitored connections (like disconnection or connection to the network) it will perform any tasks that are configured for the even that has occurred.
Currently tasks, that can be performed are:
If you frequently switch your Mac between connected and disconnected mode, you may want to use MacIfMon to start your network-intensive applications only when you are connected to network. For example you could configure your MacIfMon to start Mail application when your GPRS or LAN connection goes up, but, to conserve bandwidth, make it to start your Skype and BitTorrent only if you are connected to LAN.
In many situations MacIfMon can also speed-up your login process - if you use the configuration described above and log into the system without any active connection, none of above applications will be started thus making the login process faster.
I personally use it to activate operating modes of WWWOFFLE proxy.