The best alternatives to Harness are Copycat, Usetrace, and Testfly. If these 3 options don't work for you, we've listed a few more alternatives below.
What do you think of Harness?
Postman Recorder by DevTools— Export Postman APIs from browser
This extension is built to ease creating web tests. It is like Selenium-IDE, but for jest-puppeteer (for now). Also, this extension records actions on your browser, so it doesn't need to open up a new Selenium or Puppeteer window to record your actions on it.
Testfly is a tool to hire thousands of verified testers from 150+ countries at a cost of just $1. Over 65,000 verified testers will use your app/site, test the requested features and submit a detailed feedback report with screenshots or video captures.
Svatah is a scalable, robust, cloud based test automation platform which is imbibed in the behavior driven philosophy. Svatah enables you to rapidly design your test in a language agnostic format and supercharges your execution.