Scott (@scottsweb)

Fillet adds a new IFrame button to the toolbar in the WordPress visual editor. By using a <a href="https://codex.wordpress.org/Shortcode" rel="nofollow ugc">shortcode</a>, it allows for safer, responsive and future proof embeds.
The chosen width and height for an IFrame embed is converted into a ratio which is used to scale your embeds across different devices.
<a href="http://scott.ee/" title="WordPress web design Hampshire" rel="nofollow ugc">a plugin by Scott Evans</a>

fillet

Safely embed responsive IFrames in the WordPress text editor.

Ryan

iframes get a bad wrap, and rightly so in many cases. But when you want to embed 
one website inside of another one in a single step, they’re a really easy way to make it work.
<h4>Usage</h4>
Inside whatever post or page you want to embed another site, use the short code
[iframeWrapper url=http://example.com]
This will put an iframe linking to example.com into your page. The width will 
be 100% of the contain it’s in and the height will automatically adjust to the 
contents of the frame.
This plugin was originally written to embed <a href="http://www.proofbuddy.com" rel="nofollow ugc">ProofBuddy</a> 
sites within a WordPress theme without much fuss. But it should work well to embed 
any site within a WordPress theme.

iframe Wrapper

A small little plugin to embed an auto resizing iframe into a WordPress page or post.

fillet vs iframe Wrapper