The analyser is only available over the web, but it's free. there's a basic version and a more advanced version in the Member Area. Lexical density looks at the number of different words as a percentage. If I write a single sentence, every word may be different, so that would have a lexical density of 100%, but as I start repeating the density falls. grammatical words, which account for a huge amount of repetition, bring the score down. also, if I write about 'John', I will repeat his name, which will lower the density. The higher the density, the higher the vocabulary load. the Fog index is a method calcualting the number of difficult words, etc, to try to see how difficult a text is to read.
