BuddyPress.org

The chat will be awesome. Also another option for simple “Who’s online” is to check for all users that have the usermeta of “last_activity” set for something within the last 5 minutes.

Quite simple really:

if ( time() <= strtotime( '+5 minutes', get_usermeta( USER_ID, 'last_activity' ) ) )

// This user is online.

else

// This user is offline.