As far as I'm aware this is not possible out of the box.

Hi,

It depends how far you place OOTB

OOTB, there is an API which let you use Workflow Services.

https://msdn.microsoft.com/en-us/library/office/dn481315(v=office.15).aspx

By this way, you're able to build a JavaScript in order to get workflow instances and pop a message to users on page loading.

But they are not Nintex considerations, only basic SharePoint capabilities.

The problem is that Workflow runs in "back-office"...so it can't act on user screen.

The only way to do what you want is develop something on a specific page (javascript or something as Pierre said)....then the popup will only appear if user goes on the corresponding page.

The more efficient way should be to use native NINTEX features that communicates with specific programs, wich are able to pop : email sending, or Skype/Lync notification.

Hi,

Does the user need to click OK for the workflow to continue? Or is it more of a progress report you're after?

Thanks

Jan