Which language learning platform first introduced the 'freemium' subscription model with a streak-based gamification system that rewards daily practice?

In the evolving world of language learning technologies, subscription models have transformed how people access linguistic education resources. Different platforms have pioneered various approaches to monetization and user engagement. This trivia question tests your knowledge about a significant innovation in subscription pricing that changed the language learning industry. Do you know which company first implemented this groundbreaking model?

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Duolingo
Rosetta Stone
Babbel
Memrise