If you want to allow site visitors to Sign In, leave comments or feedback or want them to review others feedback then you can do it by adding a GUESTBOOK in your peperonity site.
First LogIn your peperonity account, then come on Site Editor, click "Add a Page" then click "Guestbook" and then click 'Add guestbook'.
N.B.: Please keep an eye on your guestbook and delete inappropriate entries yourself.
