Slipping Away Users plugin is available in Enterprise and Community Editions. If you'd like to see it in action, you can sign-up for an Enterprise Edition trial or setup your own Community Edition instance.
This plugin reports number and percentage of users who didn't have a session in your application for more than 7, 14, 30, 60 and 90 days, in buckets. You can also display individual users in each bucket using user profiles.
How to find slipping away users and regain them