All software listed on this webpage is free to use. Some have their source code available for modification, while others provide only the executable, possibly accompanied by DLLs. If the source code is not available, it is likely because the software is part of a larger project that will evolve into a product in the future.
IDK Parser is a Windows command-line tool that lets you check IDK files, view error messages, and convert them into HTML files. It can generate a valid HTML website; in fact, this very website was built using it.