Download DICT Development Group for free. Client/server software, human language dictionary databases, and tools supporting the DICT protocol (RFC 2229).
Download Artha ~ The Open Thesaurus for free. Artha is a handy thesaurus based on WordNet with distinct features like global hotkey look-up, passive desktop notifications, regular expression based search, etc.. Artha may be used as a free open-source replacement to the proprietary WordWeb Pro.
Download GoldenDict for free. A feature-rich dictionary lookup program, supporting multiple dictionaries' formats, perfect article rendering with the complete markup, illustrations and other content retained, and allowing to type in words without any accents or correct case.