Next up is something that has nothing to do with simplicity, but instead usability. Most Mac applications have support for what's called applescript. It's quite easy to learn, as it is written in English. An example of a script:
tell application "Adium" to go away with message "I'm sleeping" #Sets away status to Adium
delay 3600 #Waits for an hour
tell application "iTunes" to pause #Pauses the playback on itunes
This is a simple use of the script editor to create a “sleep”-script, but it can also be used for much more advanced functions.