Mark posts as significantly updated an display them in a widget.
WP lastupdated lets you easily add a shortcode or widget to you site which tells your visitors when the last time your site was updated.
This plugin generates customizable messages stating the last modification date and time for the whole site and the individual content (if appropriate)
Displays the last updated date for all plugins in the WordPress.org plugins repo.
This plugin adds a column to the admin plugin's page to show when each plugin was last updated.
Use Post Updated Date Plugin to Add Last Updated Date in WordPress Blog Posts.
Displays Plugin Modification/Updation time. Useful when you have multiple plugins, and you are not sure which plugin is last modified.