Which language learning product innovation first successfully implemented 'spaced repetition' technology to optimize vocabulary retention?

Innovative language products have transformed how we communicate across borders, learn new languages, and express ourselves. Behind these tools are fascinating stories of product development, linguistic research, and market disruption. This poll tests your knowledge about a groundbreaking moment in language technology product history that changed how we approach language learning and translation.

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Rosetta Stone's Dynamic Immersion methodology (1992)
SuperMemo software by Piotr Wozniak (1987)
Duolingo's gamified learning platform (2011)
Babbel's context-based learning system (2007)