PocketMod is a very cool little trick, whereby you can turn a single sheet of paper into a small, multipage notebook with a few careful folds and one cut of your scissors. And the PocketMod, the website, makes it even easier to design your own little notebook.
The site offers a wide variety of page templates which you can drag to any one of the 8 pages of an assembled PocketMod notebook, including calendars, writing guides, organizers, and many others. Design your PocketMod in your browser, choose the paper size (8.5x11 by default) and send it to your printer.
If you're not familiar with how to fold a PocketMod, there's even video instructions available. People have even used PocketMod to create little booklets for specific purposes, like this retro self-help notebook.
Whether you find it useful or not, you have to admit that PocketMod is a very clever design.