Ooh. I love mini post-it notes. So…I’m your first customer for a tear off wrist wearable calendar.
Add a light and it’ll be as popular as fidget spinners in 2 weeks.
I have one of these - well, sort of; it has a trivia question on the front, and the answer on the back.
Each day, I tear off the previous day’s sheet to reveal the current day - the whole point of a daily calendar is to know what “today” is - then read what’s on the back of today’s page.
Not just for tear-off paper calendars.
I know somebody with a calendar made of plastic cubes.
It looks like the photo in this link:
https://www.etsy.com/il-en/listing/1042898479/wooden-block-perpetual-calendar-set-desk?ga_order=most_relevant&ga_search_type=all&ga_view_type=gallery&ga_search_query=cube+calendar&ref=sr_gallery-1-4&content_source=c8db8e324ea7416d8f78f57badbc97bd3ae538b6%253A1042898479&organic_search_click=1
For this guy, using such a calendar is truly a precision art.
EVERY frickin’ day of his life, he has to rotate the cubes to the next day. And apparently, he has never failed. Every single time I see his desk, the cubes are correct.
Why he bothers, well…I dunno.
Yes, we do accept pre-orders. $500 for our precision tear-off WristCal; $650 for one with a light; $1000 for our ruby encrusted model. Hey, it’s cheaper than a Rolex…even cheaper than a Rollex.
Gimme a minute. Gotta check under couch cushions. 
I’m pretty sure that at one time 3M made a wrist-mounted Post-it dispenser. So a simple wristband with a built-in plastic holder that dispensed little Post-its. Not so different from the wrist-mounted pincushions seamstresses used to have.
Current searches don’t find the thing, so I may be misremembering. This was long ago, back in the heyday of the paper-powered offices.
But I’m sure you’d have loved this thing (if in fact it had ever existed).
Got one or two.
**
They now have magnetic pincushion thingys. Those are fun.
I love my doohickeys.
Note that this works only if the digits are in a typeface where the 6 can be turned over into a 9.
It’s not that difficult:
One cube has 0,1,2,3,4,5, and the other has 0,1,2,6/9,7,8
Starting from 01, the two cubes switch places on the 6th, 10th, 16th, 20th, and 26th of each month, and on the 1st of the next month.
I’ve been enjoying this thread so thank you for starting it.