Here’s a short video showing some of the differences between Apple’s own Script Editor and my DisplayDroid.

If you haven’t got 5 minutes, the highlights include:

DisplayDroid shows result of each line of the script
DisplayDroid offers more informative error messages
DisplayDroid has automatic language detection (between AppleScript and JavaScript)
DisplayDroid allows you to set a breakpoint on any line in your script
DisplayDroid lets you step through the script line by line