Crowdin - Localize your product in a seamless way
Glosbe - Huge collaborative massively multilingual dictionary.
POEditor - The translation and localization management platform that's easy to use *and* affordable!
Visuwords - The fun and free way to look up definitions. THE graphical dictionary and visual thesaurus.
Lokalise - Localization tool for software developers. Web-based collaborative multi-platform editor, API/CLI, numerous plugins, iOS and Android SDK.
Wordnik - the biggest online English dictionary, by number of words