Of all the scripts you are using or have used in the past, what's your most favorite one? I'm don't mean custom scripts of course, but scripts that can be purchased (or perhaps even freeware scripts).
Please mention the name of the script and what it does. I think it will be interesting to hear what you all like. My favorite one would be vBulletin I think. It's a forum script, but I think you all know it since you're looking at it now
