The best alternatives to Capptivate are UXArchive, Pttrns, and Use your Interface. 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
UX-Archive is powered by Waldo, the world’s first no-code testing platform that lets anyone create reliable, automated mobile tests without the hassle of scripting.
Hand-picked collection of Android apps screenshots with mobile patterns for your inspiration. You could filter by pattern type or element of the interface.