Glosbe - Huge collaborative massively multilingual dictionary.
GoldenDict - The program has the following features: Use of WebKit for an accurate articles' representation, complete with all formatting, colors, images and links.
Wordnik - the biggest online English dictionary, by number of words
Lexpanse - 2450 free basic offline dictionaries in 50 languages available for download.
Visuwords - The fun and free way to look up definitions. THE graphical dictionary and visual thesaurus.
Dicty - Dicty is a viewer application for dictionaries in StarDict format.