The volunteer project OpenTaal (Dutch for "Open Language") develops Dutch language resources such as a (certified) spell checking word list, hyphenation patterns, thesaurus and grammar checking materials. Although these are primarily intended for use in open source software such as OpenOffice.org and Mozilla Thunderbird/Firefox, we use liberal licenses that make it possible to use the materials in closed source software as well. The foundation Stichting OpenTaal was founded to support this work.