org.languagetool:languagetool-core (maven): LanguageTool is an Open Source proofreading software for English, French, German, Polish, Romanian, and more than 20 other languages. It finds many errors that a simple spell checker cannot detect like mixing up there/their and it detects some grammar problems.
Keywords: grammar|natural-language|natural-language-processing|proofreading|spellcheck|style-checker