When comparing NinjaMock vs UX-App, the Slant community recommends UX-App for most people. In the question“What are the best mockup and wireframing tools for websites?” UX-App is ranked 26th while NinjaMock is ranked 27th. The most important reason people chose UX-App is:
UX-App uses a drag and drop puzzle like JavaScript representation. Unique and expressive
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Online player
Pro Online collaboration
Pro Easy to use
Pro Intuitive
Pro Rich collection
Pro Multiple platform support (web, mobile, etc.)
Pro Prototype with graphical JavaScript
UX-App uses a drag and drop puzzle like JavaScript representation. Unique and expressive
Pro Mock up & prototype in the browser
Allows you to mock up with real HTML, and present expressive prototypes in the browser. Has lots of conveniences like team chat, notes, and a share link to present prototypes.
Pro Long free trial & cheap subscription
It's possible to start without creating an account. Creating a free account extends the trial, and the memberships are cheap @ $5/month.