What are some alternatives?
When comparing UsabilitySquare and UX Flow Wireframe Prototyping System, you can also consider the following products
UXtweak - Online user testing and usability platform
Userflows - Automatically generate user journeys
ProtoPie - ProtoPie is the easiest tool used to turn your UI/UX design ideas into highly interactive prototypes for mobile, desktop, web, all the way to IoT.
Usabilla - Collect user feedback and improve your websites, apps and emails with Usabilla's Voice of Customer Solutions.
Whimsical Wireframes - Lightning fast wireframing with real-time collaboration.
UsabilityTools - Where UX meets Conversion. Unlock the Potential Behind Remote Research and Testing