There are plenty of desktop publishing options out there for those who want to create magazines and newspaper layouts, but precious few that specialize in just booklets.
CocoaBooklet does though, making it simple to create mini booklets or manuals in PDF format. Each booklet is limited to eight pages, however, so you'd better make sure that whatever you're writing is brief. It works simply by printing two sheets of paper with everything on, which you then have to bind in a way which makes eight different pages.
On the first sheet, you'll find pages 1, 2, 7, and 8 and on the second sheet you can print pages 3, 4, 5 and 6. Once printed, you just have to staple it in the middle, fold it in two and your booklet is created. In addition to this, CocoaBooklet allows you to print directly to PDF enabling you to send the booklet by email. However, this app does not work on Snow Leopard yet after Apple removed Cocoa-Java components in the new OS.
CocoaBooklet is a very limited application, but ideal for anyone who regularly writes mini guides or manuals.