A convenience sample of documentation tools or tools that document and structure certain necessary activities for software development...
Swagger for RESTful services (open or free license)
thucydides for TDD with WebDriver/Selenium 2 (open or free license)
JSONDoc (open or free license)
Doxygen for generating reference/documentation via annotated source code for most programming languages (open or free license)
RedGate for SQL schema visuals and doc and other things (commercial license)
DocBook a general purpose XML and SGML document type for documenting anything/everything (open or free license)
PerlPod a markup for writing reference/documentation for Perl code (open or free license)
Javadoc a markup for writing reference/documentation for Java code (open or free license)
Sandcastle a help file builder for Windows (open or free license)
Cucumber a Ruby tool that takes the Behaviour Driven Development (BDD) philosophy for describing application functionality that maps into code (open or free license)
