The French Republican Calendar and Day Images
I recently came across and interesting historical calendar called the French Republican Calendar. It was an 18th Century attempt to create a decimal-based calendar. The interesting part of the calendar from a memory techniques point of view is that every day of the year had a unique name like “grape”, “saffron”, and “chestnut”.

The Art of Memory Wiki has lists of the day names.
One of the interesting aspects of having an image for every day is that it would create a peg to attach information to. Even after 10 years, one would only have 10 memories attached to a single peg image like “grape day” or “saffron day”.
I haven’t tried this technique, but thought that readers might be interested in experimenting with it.
Read more on Wikipedia.