<!> Hunspell] [http://en.wikipedia.org/wiki/Hunspell is originally an advanced spell checker software, most famously used for spellchecking in the OpenOffice suite.
In Solr, Hunspell is currently used for stemming. The project originated at Google code but was contributed to Apache in Solr3.5.
Hunspell is both dictionary and rules based, using the same dictionaries (.dic) and rules files (.aff) as those in OpenOffice. These dictionaries exists for 99 languages - downloaded dictionaries here or here.
See HunspellStemFilterFactory for details about how to configure Hunspell in your analysis.