User card is displayed when you hover over a username. This feature is currently available on the dashboard "on-call widget", task history logs, rota day view, opportunity managers list and event managers list.
It adheres to the logged in user permissions, e.g. you shouldn't be able to send a message or view an address if you don't have permission to.
Also, you must have the Assign task to others, and the user must have the Assigned to a task permission to see this option under the Actions drop-down.
If a user is available, a green banner will appear at the top right of the card; hovering over the banner will display the remaining time the user is available.
If a user already has assigned tasks that are due today, a yellow dot will display next to the user name. Clicking on the dot will redirect you to the task listing page filtered by the assignee.
Click here for more information on creating tasks and assigning to others.