Scott Werner

When inserting an image into a post, WordPress uses absolute URLs to the files. This plugin overrides that functionality and forces it to use relative URLs.
For example:
WordPress Default: 
http://www.example.com/wp-content/uploads/2013/04/example.jpg
Plugin Override: 
/wp-content/uploads/2013/04/example.jpg
This is particularly useful if you plan on switching domains ever as well as reducing HTTP requests.

Relative Image URLs

Creates relative URLs for images when inserting into posts.

alastairbrayne

Create custom menu items with links relative to the root url of the current wordpress installation.
Simply add a custom link as normal with the url prefixed by %ROOT%. e.g. to get http://mydomain.com/wp/myCustomPage if your wordpress lives at http://mydomain.com/wp then you just write %ROOT%/myCustomPage for your link url.
<h3>Relative Menu Item</h3>
Create custom menu items with links relative to the wordpress root url.
<h3>Important Notes</h3>
Not tested with multisite installations.

Relative Menu Item Plugin

Create custom menu items with links relative to the root url of the current wordpress installation.

Relative Image URLs vs Relative Menu Item Plugin