Artha is a handy thesaurus based on WordNet with distinct features like global hot key look up, passive desktop notification, regular expression based search, etc. Artha may be used as a free open-source replacement/clone to the proprietary WordWeb Pro thesaurus (which is also based on WordNet) on Unix-like and Windows operating systems.
HogTrans provides an automatic word translation engine built on statistics of text translations used for free software. It basically provides an automatically created dictionary with multiple translations and example usages for each. HogTrans can import translations from standard GNU .mo-files.