I know there are:
This is the first time I'm seeing a website with .sd at the end. What exactly does that mean and is there a wiki that explains a bit more?
For example, this website: http://www.racingpost.com/horses2/results/home.sd
First time I'm seeing it and I'm just curious.
Edited for the url you added: that specific one is most likely being used with the BlueDragon system, a family of runtime server-side products for the deployment of CFML pages, deployed in possibly a j2ee environment.
for instance you can google the site for references:
http://www.google.com/search?q=site%3Anewatlanta.com+%22sd
or see a servlet debug page:
or you may be referring to the TLD (top-level domain name).
the TLD .sd belongs to country of Sudan which is managed by the Sudan Internet Society:
Because the choice of extension is practically meaningless on the web - the content-type header defines the actual format of the content - there are lots of exotic extensions around, mostly defined by the CMS or framework used. I'm pretty sure this is not an "own format" in the sense that "html", "aspx" and "php" differ from each other internally by containing raw HTML, PHP code, or ASP code, but just a "vanity extension" if you will.
Can you show us the web site in question? Maybe somebody can hazard a guess what CMS/platform it was built with.
.sd could be anything. According to Fileinfo.com it is the default extension for some type of audio file.
However, I could make a php page called index.sd and as long as I have my webserver configured in the correct way, it would serve it up as php. That goes for other things as well, .html, .py, .pl... etc, etc.
I would just need to add this to my configuration file for apache:
AddType application/x-httpd-php .sd
According to fileinfo .sd is an audio file.
The Top Level Domain .sd denotes Sudan.
Other than that, you can come up with any extension you want (or even use an existing one) and point it to any handler you want, say, in your web server, or in your code. (In the .NET world, you can define your own MIME types through IIS, or setup Http Handlers in your web.config)
At a guess, it's probably one of the above - it's pretty trivial to get a webserver to arbitrarily treat a file as whatever you want irrespective of its extension.