While there is no free software that can analyze words of a sentence and automatically place them in a diagram, some websites offer free downloadable software to make drawing neat diagrams easier. Baruch College and the University of Central Florida offer such software.
The free programs from Baruch College and University of Central Florida allow users to drag the words of a sentence onto a diagram picture and print it. Baruch's program color-codes the parts of speech for visual comprehension. Websites such as zzcad.com break down sentences into each word's function, such as noun, verb and adjective, although it doesn't diagram the sentences.