The best alternatives to NinjaMock are Balsamiq, Free Device Mockups, and Mockup World. If these 3 options don't work for you, we've listed a few more alternatives below.
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AssemblyAI— Speech-to-Text API with superhuman accuracy
Imagefactory.io harnesses the full power of 3D software to produce unique, personalised, photo-real images for your business. You can inject names or words into pictures, or project images onto products.