Cypress looks interesting as an all-in-one solution for test runner + paid remote executor service. Similar builtins to WCT (Mocha, Chai). WCT was attractive for us as an open-source runner in that it isn't tied into any company's product; while it comes with good out-of-the-box support for running on Sauce Labs via standard tools (sauce-connect), there are also ways to use it with Browserstack and has a plugin system. Feels like a more generic pluggable building block for testing and less locked in to a particular vendor.