一些常见的NLP任务的开源/免费工具，

*Computational Linguistics Toolbox
CLT http://complingone.georgetown.edu/~linguist/compling.html
GATE http://gate.ac.uk/
Natural Language Toolkit(NLTK) http://nltk.org
MALLET http://mallet.cs.umass.edu/index.php/Main_Page

*English Stemmer
Snowball http://snowball.tartarus.org/

*English POS Tagger
Stanford POS Tagger http://nlp.stanford.edu/software/tagger.shtml
TreeTagger http://www.ims.uni-stuttgart.de/projekte/corplex/TreeTagger/

*English Parser
Stanford Parser http://nlp.stanford.edu/software/lex-parser.shtml
Berkeley Parser http://nlp.cs.berkeley.edu/Main.html#Parsing


*English Keyphrase Extractor
KEA http://www.nzdl.org/Kea/index_old.html


*English Name Entity Recognizer
Stanford NER http://nlp.stanford.edu/software/CRF-NER.shtml

*Chinese Word Segmentator
中科院ICTCLAS http://www.nlp.org.cn/project/project.php?proj_id=6
Stanford Word Segmenter http://nlp.stanford.edu/software/segmenter.shtml

*Topic Modeling Tools
Matlab http://psiexp.ss.uci.edu/research/programs_data/toolbox.htm

*Machine Learning Methods
CRF++ http://crfpp.sourceforge.net/
LIBSVM http://www.csie.ntu.edu.tw/~cjlin/libsvm/

*Search Engines
Lucene http://lucene.apache.org/
中科院FirteX http://www.firtex.org/

*Data Mining Toolbox
Weka http://www.cs.waikato.ac.nz/ml/weka/