Duolingo, a Pittsburgh-based language learning business last valued at $2.4 billion, has officially filed to go public. The 400-person company, which we explored in great detail in our EC-1, was co-founded by Luis von Ahn, the inventor of CAPTCHA and reCAPTCHA, and Severin Hacker. One of the most revealing bits of its story? It’s a … Continue reading Duolingo filed to go public