Common open-source/free NLP tools

Some common open-source/free tools for NLP tasks,

* 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
Chinese Emy of Sciences 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 Co http://lucene.apache.org/
Chinese Emy of Sciences firtex http://www.firtex.org/

* Data Mining toolbox
WEKA http://www.cs.waikato.ac.nz/ml/weka/