DeadC.net is a link shortening service with a difference. You can create a URL that can only be clicked upon once.
Of course, it’s only a re-direct, so someone can always copy the redirected URL, but useful for quickly sharing things “without being tracked,” as the site says.
In many ways, this is horribly wrong, because it breaks the fundamental principle of avoiding dead links on the Web, but that’s the idea I suppose.