WP Monitor is a WordPress plugin I wrote that is used to monitor the vital signs of a site and it give the user important information that is needed to properly administrate the site, all in a way that is easy to read with gauges and indicators.
It offers a lot of useful information that may not be site-specific, but that a developer would want to know at a glance. The PHP version, the database version as well as the number of updates and the number of inactive plugins are among the stats shown by WP Monitor.
Since publishing this post I have retired WP Monitor from the WordPress plugin repo. I do want to mention that the "health monitor" feature that was added to WordPress Core after I made this plugin is the same concept as this plugin was but more detailed. I'm not saying anyone copied me but the idea was so good apparently they wanted something like it built-in to WordPress.