This plugin is a lot like the com4guests plugin by esclkm, but that wasn't working for me, so I wrote a new one.
Open Comments allows your guests to post comments on your pages, just like registered users. The only difference is that guest have to provide an email address, and optionally a website address. This is similar to Wordpress. For security, the plugin can use reCAPTCHA. It also has the option to send an email to the administrator when a new guest comment is posted.
Installation:
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