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.
Usage
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 ProofBuddy sites within a WordPress theme without much fuss. But it should work well to embed any site within a WordPress theme.