The first beta of DisplayDroid is, for a limited time, freely available to anyone interested in testing (requires Yosemite, 10.10). DisplayDroid executes an AppleScript or JavaScript whenever you connect or disconnect an external monitor, primarily with the intent of automatically setting up the environment depending on your display status. DisplayDroid includes its own script editor and a number of presets (i.e., built-in scripts) to get beginners started.

Full details of DisplayDroid can be found here: http://sqwarq.com/displaydroid/ To get a free beta copy of the app, please register for the Community forum here: http://displaydroid.proboards.com and I will email you a beta copy of the app in the next few days.