Track all the activity in the com_users component, made by the users themselves or by your admins and site managers:

-User logins
-User registrations
-Admin backend logins
-User profile edition
-User creation (by admins)
-User deletion
-User logouts

Make rankings of Most logged in users and, of course, combine the results above selecting your desired timeframe, in the "relative time" mode:

-Last hour
-Last 6 hours
-Last 12 hours
-Last day
-Last 3 days
-Last 5 days
-Last week
-Last 2 weeks
-Last month
-Last 6 months
-Last year
-All time

Or in the "absolute time" mode:

-Today
-Yesterday
-This week
-Last week
-This month
-Last month
-This year
-Last year

Show evolution of:

-User logins
-User registrations

Combine the list above with any of the possible filters:

-Current user
-Specific user
-All users (equivalent to no filter)

And, of course, combine the two lists above selecting your desired timeframe, to complete the chart's x-axis to show the items evolution:

-Last X days (define the number of days you want to consider)
-Last X months (define the number of months you want to consider)

Make complete user reports on the backend showing who logged in and when, who registered, etc. Make beautiful graphics and charts from your reports to have a quick and intuitive view of you user activity stream in your site!

Many graphic charts available:
-Line charts
-Area charts
-Column charts
-Pie charts
-Stepped area charts
-Line charts (smooth)
-Column stacked
-Area stacked
-Map charts

IP geo-location to filter your users by Country, make full location based reports!