Most websites have a contact form that sends the webmaster e-mail. Writing a contact form is quick and easy, writing one with good security is not.
An app that did nothing but make a solid contact form would be useful. The functional elements are very standardized: from field, reply-to field, optional drop-down giving a choice of topics, text field, submit button. It could be customized with CSS or whatever.
There exist many commercial programs to do this, but I haven’t seen an open-source one. Have you?