The Contact Form will work in any "html" stacks page, and will not require you change the page extension to "php", nor will it force the "php" extension.
The form is fully responsive for use in responsive theme designs.
This has the benefit of not changing the location of your existing page when published. Imagine you have a published a page "www.mypage.html". In the past, adding a form stack would have required you change your page extension to "www.mypage.php". This would mean the anyone that had bookmarked the page, or any search engine that had listed the page, would no longer be pointing at the updated page after you re-publish. Contact Form, keeps the extension as "html" so does not change the location of the page on your server.
As well as that the stack has : Auto Responder option. Anti Spam measures. Very simple colour choice for the theme of the form. And a what you see is what you get type edit area interface.
NEW..! HTML signature support in the auto response email.