Roget's Thesaurus of English Words and Phrases was written in 1911. It organizes English words and phrases by abstract concepts.
This spelling checker is an interface to GNU Aspell.
Analyze short English texts: spell check, diction, readability, and word frequency count.
This is an interface to the WordNet-3.0 lexical database. Word meanings are organized in a semantic network. It produces a lot of output for each word.