Weighting in at the size of a business card, the tiny Thumb Calendar makes it possible to keep a calendar on you at all times. The Thumb Calendar is two sided and in order to use it, you must cover the dates that are not directly below the month header with your thumbs. The designer only has a PDF version for 2007 on his homepage, but you can grab a 2008 version from Flickr (linked below). The Thumb Calendar is a free download and makes a great addition to any purse or wallet.
Tiny Business Card Calendar [Calendars]