1st Step:
Create a file e.g. "monthminiview.tmpl" somewhere in your fileadmin directory e.g. fileadmin/templates/cal/
-> fileadmin/templates/cal/monthminiview.tmpl
2nd Step:
Insert data into the file:
-> ###MONTH_SMALL|+0###
Note: "MONTH_SMALL" reflects the template "+0" the monthly offset from today. Have a look at the sidebar.tmpl at your cal installation (static/template/sidebar.tmpl) and search for "MONTH_SMALL". You will find 3 marker with -1 (last month), +0 (this month) and +1 (next month)
Save the file.
3rd Step:
Modify your template or create an extended template for cal.
You have to assign the new template to a view and set this view as default view
plugin.tx_cal_controller.view.month.monthTemplate = monthminiview.tmpl
plugin.tx_cal_controller.view.allowedViews = month
plugin.tx_cal_controller.view.day.dayViewPid = //insert pid where to display the events for a day (else they won't get displayed at all)
plugin.tx_cal_controller.pidList = //insert a comma separated list of pids containing your events here
4th Step:
Insert the calendar plugin as content element on your page
That's it. Have a look at you page :)
// PS: since cal 0.16.0 this option has been included in the flexform. Have a look at month view -> Display as a mini calendar