External Header Footer is a simple WordPress plug-in that exposes that site’s header and footer over HTTP as URLs whose content can then be consumed.
How is this useful? Let’s say you’ve got a WordPress website at your www subdomain, and a forum for your community of users at a forums subdomain. In many cases, you’ll want to keep the header, footer and basic styling (link, text, background colours) of both sites identical.
That’s the cue to use External Header Footer: Once this plug-in is enabled on www, run a scheduled task on your forums subdomain to retrieve and locally store (write to a file, or to memory) the header and footer to be displayed on that site every day/hour/week. Now with minimal effort you can be assured that both sites will maintain a consistent look and feel.