Each calendar date has one historical entry. Entries follow America/Denver time, change daily and repeat annually, including February 29 in leap years.
Historical entries are selected from Wikipedia contributors through the wikipedia-onthisday dataset. Each entry links to its source date page. Wikipedia-derived text is available under Creative Commons Attribution-ShareAlike 4.0. The selection is also available under that license. No endorsement is implied.
The September 11 entry is original commemorative wording with a link to the National September 11 Memorial & Museum. The collection is edited for selection and presentation; it is not an exhaustive history of each day.