This is a plugin for the Open Source Web Analytics platform Piwik. If enabled, it will add three new widgets that you can add to your dashboard.
At the moment the plugin defaults to maximum concurrent usage for every 5 minute time interval for the last 200 days. These numbers can be reconfigured in the plugin settings page of the user profile menu.
One widget gives a single number representing the maximum number of concurrent users that have ever occurred in the N time interval over the last M days. The other two widgets are a line graph and a table showing the maximum concurrent visitors for each N time slice of 24 hours over the last M days.
The plugin borrows the code structure and an SQL query from the Barometer plugin built by @halfdan.
The plugin has also been translated into Ukrainian and Russian by twixi