This is a This Day In History management plugin and widget which you can use to enter and display historic events.
Installing is pretty easy takes only a minute or two.
Upload 'this-day-in-history' directory to your '/wp-content/plugins/' directory.
Activate the plugin through the 'Plugins' screen in WordPress.
On the 'Widgets' sub-menu of 'Appearance' you will find a new widget type called 'This Day In History'; alternatively use a shortcode in a post or page.
Add this widget, to your themes widget display areas, select a title and click Save.
Enter historic events via the new 'Historic Events' admin page. These will be automatically displayed by the widget on the anniversary of the day that they occurred.