Clicking on a user mention shows other mentions. But maybe we want to interact with that user in other ways, like sending a message (which should open the private conversation with them), send an email, view profile, etc.
In addition, we could allow for integration with some other service. For example, integration can be defined as a URL endpoint that can pass/post the username as parameter or request a custom field in the use profile which then can be sent as parameter. For example, let's say we want to integrate with Skype to call the user via Skype. Integration might look like this:
Display Name: "Call with Skype"
Custom Field: "Skype username"
URL end point: "skype:%custfield%?call"

Such integration will now show on each user profile a new field to fill up if desired: "Skype username". Then in the context menu of the user, we will see option "Call with Skype". Clicking on that option will do an intent/open url that matches "skype:<value that user entered in the custom field>?call"