The best alternatives to Challenged are Rival.ly, Trendoline, and Moro. 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
Rival.ly is the first social video sharing app that allows users to compete head-to-head through short/semi-short videos while leaving the victor up to the masses. Users can join in on daily challenges from your favorite influencers to earn profile upgrades and more. We will be adding Live-challenges, music and short-form news feed soon!
Start a group. Invite all your friends. Make up a challenge. Complete the challenge as creatively/best as possible. Send it to the group. When everyone send something, rate each other. The highest average rated player may come up with the new challenge.