Our neighborhood calls it ghosting -- and we start October 1st.
Ghosting/booing is when one neighbor fills a basket or bag of halloween goodies for another neighbor, rings the bell, and leaves the goodies anonymously. The recipient hangs a ghost on their door to show they've already received, then ghosts/boos someone else until all participating families have been visited. It's fun. The kids look forward to the doorbell ringing, but love to drop the goodies and run even more!
Our neighborhood sends out an e-mail in September asking who wants to participate, so only "participating families" are ghosted. A list goes around with the basket so everyone knows who they can choose from. However, I know of other neighborhoods who do it more like a chain letter. You don't sign up, it just happens... then you're supposed to "continue the chain" to other families.