Who has been logging in?
This a simple bash one liner to get a listing of who has logged in when, discounting multiple logins in one day. It gets this information from the log file. If you rotate the logfile monthly (the default with dhis2-tools for example) you can easily create monthly reports.
or operating on a rotated gzipped file
Who has been entering data? This one is a simple query to the database. You could make it fancier by grouping by district or the like: