TL;DR: It's the same as Amazon Mechanical Turk, but aims for higher quality by screening the people performing the tasks.
Our main focuses for our product are around high quality, ease-of-use, and reliability. In our experience, MTurk exhibits none of those.
It requires a lot of work to get truly high quality results, and virtually impossible above a certain quality threshold. MTurk promises no SLAs and forces the customer to do a lot of work such as price discovery, building UIs, and quality control, not to mention how difficult to use their API is. Our philosophy is handle all of that complexity for the developer.
We've been inspired by our own experiences using easy-to-use APIs like Stripe, Twilio, SendGrid, etc., and wanted to build a similar experience for human intelligence. Hope that helps!
Scale is vertically focused, currently focusing on image annotations and audio transcription. This allows us to provide extremely high accuracy and an ever-improving developer experience by investing heavily in tooling, automation, and screening. It's very difficult to do that as a more generic crowdsourcing service.
We're also entirely developer-focused as a company. Our users are engineers, and we have a singular focus to provide the best experience in using Scale to build more complex products.