The Jake Group

The purpose of this plugin is to facilitate deployment of subdomain links to 
landing pages on a WordPress website. The plugin automatically maps subdomains 
to page and post permalinks based on the post_name field in the database. 
There are no administrative settings.
This plugin DOES NOT edit DNS zone files. Subdomain DNS records themselves 
either need to be set up individually or as a wildcard record in the DNS zone 
file to map to the website directory. Once the request reaches the WordPress 
system, the plugin will automatically check to see if the subdomain matches a 
page or post name. If so, the WordPress query is edited to get that page/post 
at its permalink. The WordPress siteurl is excluded, as is the naked 
second-level domain.
Example mappings:
URL → Mapping 
http://example.com → default homepage (no remapping) 
http://www.example.com → default homepage (no remapping) 
http://test-page.example.com → example.com/test-page/ 
http://mypost.example.com → example.com/mypost/

Automatic Subdomains

Automatically maps subdomains to page and post permalinks based on post slug.

DragonOfDev

<ul>
<li>On “add post” page there will be a checkbox, “Fake Subdomain”</li>
<li>When checked it uses a custom field called fake_sub to create a fake subdomain for the post</li>
</ul>

yg-Subdomains

YG-Subdomains allows users to setup there specified page as subdomains. It's a lite and fast code.

Automatic Subdomains vs yg-Subdomains