Alexa Hirschfeld bounced almost immediately out of undergraduate studies at Harvard and into the start-up world. (She worked briefly for Katie Couric at CBS News, but she quit to co-found the design-driven Evite competitor Paperless Post with her brother James in 2007 because it seemed more interesting.) She and her brother have raised at least $6 million for a fast-growing business that generates enough revenue that it became profitable last year. Strikingly, the pair was confident enough to ask users to pay for virtual currency to spend on customizable digital stationary from the first; there’s no advertising on the site.

New Yorkers in the tech scene have probably seen Ms. Hirschfeld--who is eloquent, sharp and incredibly laid-back--speak at local tech meetups or at Columbia, or they might have read about her in the New York Times, Forbes (“Women to Watch), or CNN Money (“Most Powerful Women Entrepreneurs”), or Fast Company (“Most Influential Women in Technology”).