Dropbox exists because Drew Houston forgot his USB drive on a bus trip. His fix was a special folder. Put a document in it, and the document appeared on every other computer and phone you used. That simple trick won hundreds of millions of users, most of them on free plans. When Dropbox filed to go public in 2018, it was one of the largest private tech companies of its era. The question was whether enough of those users would pay.

A Demo Video, a Waitlist

Houston started Dropbox in 2007. He and Arash Ferdowsi joined Y Combinator and built a product that hid all the hard parts of keeping files in sync. A short demo video spread widely and filled a waiting list. Their bet was simple. People would love a free product, and enough of them would pay for more space to build a real business.

Leaving Amazon's Cloud

Dropbox priced at $21 a share in March 2018, above its expected range, and the stock jumped on its first day. Before the offering, it had moved most of its storage off Amazon's cloud and onto its own servers to cut costs. In later years growth slowed as rivals bundled storage with other software. Dropbox remains a public company, still led by Drew Houston.

Cover: Sudden Shower over Shin Ohashi Bridge and Atake (Ohashi Atake no yudachi), from the series "One Hundred Famous Views of Edo (Meisho Edo hyakkei)", Utagawa Hiroshige. Art Institute of Chicago, public domain. Chosen for a sudden shower (the drop).