Zosh lets you interact with those backward folks who still depend on the fax/print/sign/fax model, or the even worse fax/print/sign/scan/print/fax model. It makes life easier for you, while those folks can even keep hanging onto their ancient technologies. When you receive an e-mailed copy of a form to fill out, you then use Zosh to tap on the fields you need to fill out. If you need to sign a form, you can use your finger as a virtual pen.
Once the form is ready to send on, you can e-mail it as a PDF from directly within the app. And, unlike with fax machines, there's no degradation in quality when you send the paperwork back.
Much of the app's form-filling functionality is reminiscent of Touch-Fill-Go. Zosh requires a digital version of the paperwork to start, while Touch-Fill-Go instead needs you to snap a photo of a hard copy with the iPhone's built-in camera (with a corresponding and unsurprising loss in quality).
Zosh costs $3 and requires iPhone OS 3.1.2 or later.
Update: The recently released version 1.1 of Touch-Fill-Go now lets you download PDFs from the Web in addition to taking a picture with your iPhone's camera.