Copydue - Top writers, on-demand for as low as $150/mo
Glosbe - Huge collaborative massively multilingual dictionary.
Mailbutler - Mailbutler adds lacking functionality to email clients and increases your productivity
Visuwords - The fun and free way to look up definitions. THE graphical dictionary and visual thesaurus.
PubLoft - Freelancer network for writers powered by the gig economy
Wordnik - the biggest online English dictionary, by number of words