I'm not aware of an add-on that does this. The data is directly track at the daily level within the xf_stats_daily table (with a Unix timestamp for the date), which you may be able to access directly to pull data out.
Active Users: (users who've logged in)
Currently we're on Vbulletin and when I run through stats on there it'll give me a html table with date and number for a date range that I can just cut and paste out and clean up in excel. Something like that would be fine but obviously a .csv download would be better.