There was this mod made by Pete T some time ago in IPS

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Keeps track of the number of registered members that have visited your site in a custom duration and also records which day you set the record for the most members online in the same day all options done via the front settings.

Its a simple widget you can place and see the list of members which have visited the site in the past X days. You determine how long is the period. Nice ego boost for admins and perhaps for other members to see that there are many users lurking around. While currently online users is always a smaller list. 😕

Sorry, that's not something what I'm interested into releasing for v4.

This was completed