KStem is an alternative to Porter for developers looking for a less aggressive stemmer. It was written by Bob Krovetz, ported to Lucene by Sergio Guzman-Lara (UMASS Amherst), and contributed to Apache Lucene/Solr by Lucid Imagination as part of 
Solr3.3
It is configured in Analysis as follows:
<filter class="solr.KStemFilterFactory"/>
See LanguageAnalysis#Stemming for more.