If you've been online for any long period of time then you probably know that Unicode is the industry standard which defines all the characters used for the text on webpages (this standard subsumed ASCII some years ago). Becuase of the complexity of the various alphabets of the world, Unicode includes specific subsets of characters for specific languages, some of which include special characters with specific accents or other alterations which might only be used by a single language group.
The following video shows the first 65537 of the Unicode characters, including the special ones, which can be displayed.
Some cannot easily show on screen, so this video can only show around 50 thousand characters (out of a total of 95 thousand, I think). Just to give you perspective, the characters are displayed once per second and this video is over 30 minutes long.
This is the work of Joerg Piringer. Why he decided to make this video is a question i cannot answer, but the video itself is pretty cool.
He also posted a text file showing all of the characters. If you make or use ebooks, I'd grab this file. It's a quick and dirty way to test for proper character support for reading apps and ereaders.
Update: A reader pointed me at another video with even more characters. This one covers 109,242 characters nd tells you what the code number is for each. And yes, I know that the first video didn't really have every single character, but if I had put nearly in the title it would not have sounded so cool.