Achoo allows you to easily view the HTML for the webpage you're viewing in Safari. It shows the HTML (as well as any inline CSS and JavaScript) with beautiful and fast syntax highlighting.

You can share the HTML you're viewing, allowing you to easily inspect it on an external device of your choosing, or send it to a friend, or simply copy it to your clipboard.

You can edit the font if you'd like it smaller to display more information, or larger if you'd like to be able to make things out more clearly.

You can also choose to edit the contents of the webpage, allowing you to make modifications and preview how they look. Changes are not permanent, simply refresh the page in Safari to return the page to its original state after you're finished previewing your changes. (Note: you're not editing the HTML directly, rather it's a visual editor of the contents of the page)

As a bonus, it includes a variety of alternate home screen icons so you can customize the app to your liking beautifully.