How to find the process listening to the localhost on OSX?
Your Mac's built in webserver is turned on.


  To Turn On: sudo apachectl start
  
  To Turn Off: sudo apachectl stop


The process you are actually looking for is httpd, the Apache server.

$ ps -ef | grep httpd  
  0 76078     1   0  3:56am ??         0:00.32 /usr/sbin/httpd -D FOREGROUND  
 70 76084 76078   0  3:56am ??         0:00.00 /usr/sbin/httpd -D FOREGROUND  
501 76139 76048   0  3:58am ttys000    0:00.00 grep httpd  


The file that is being loaded is /Library/WebServer/Documents/index.html.en, because /Library/WebServer/Documents is configured as the DocumentRoot in the default /etc/apache2/httpd.conf file that is included with OS X.