Who's behind mystery 'PrimaryArlenSpecter' site that focuses on health care reform?

I received an e-mail today letting me know about a "Primary Arlen Specter" site that is collecting names and e-mails of people who support including a public option in health care reform. The site says the following:

When we reach 5,000 signatures, we will hand deliver this letter to the office of Senator Arlen Specter.

It doesn't say who's behind it. I ran a whois search, but the site's registration is private.

(Oh, and I've saved two screen captures of the page in case it were to disappear.)

(And I'm not anonymous -- see this post from yesterday. :-)