Sequence.work is described as 'crowdsourcing platform to get high-quality data annotation, data tagging, transcription, comparison and more'. There are six alternatives to Sequence.work, not only websites but also apps for iPhone and iPad. The best alternative is Amazon Mechanical Turk. It's not free, so if you're looking for a free alternative, you could try Spare5. Other great sites and apps similar to Sequence.work are Appen (Paid), Playment (Paid), CloudFactory (Paid) and Scale (Paid).