wsdebug is a debugger for the more or less famous whitespace programming language, coming along with a rather fast interpreter (wsi).
Most programming languages like C or Perl do not care for white space characters (like tab, space or newline/linefeed). The whitespace programming language works just the other way round, don't care for any character but those white space ones.
On the whole it's just another geeky language like Brainfuck and others, however more adicting.
If you've written a whole lot of instructions you'll probably reach the point, where you get lost. Then just put your script into wsdebug and step through your bunch of whitespace instructions and watch how each command manipulates the stack (or heap).