.htaccess Action + AddHandler
This is just a very cool feature I've recently discovered on Apache servers to add custom handlers for your own custom file extensions:
Currently, I've implemented such feature to create a custom "web programming language" for one of my clients so that he does not need to learn advanced scripting languages to edit his website.
Action handler_name handler_file
Addhandler hander_name .extension
Essentially, I point my custom handler to my handler file, which is basically a parser for all files of the given extension. The parser file simply translates the simplified code into the actual, more complex code and then is outputted to the browser when the client accesses the page.
Just though you guys would like to see this. :D