What are some alternatives?
When comparing UserTest.io and Cleanmock, you can also consider the following products
Usability Testing Exchange - Free usability testing of, and feedback about, your website/app.
GluePrint - Turn design mockup into floating guide, align pixels w/ ease
UserTesting.com - Usability testing has never been easier. Get videos of real people speaking their thoughts as they use websites, mobile apps, prototypes and more!
shotsnapp - Create beautiful device mockup presentation
Userbrain - You want to improve the usability of your website? See how real people use your website for the first time, find out what works, and what needs to be improved.
Osiva - Osiva" is an acronym that stands for "Overly Simple Image Viewing