Slack, Instagram, Twitter: Side Hustles That Became Billion-Dollar Companies

Thirty years ago, when I lived in a very small town, my next-door neighbor, John, would often stand in his backyard, staring off into space, sometimes for hours.

He was a very nice man, but still: I thought it was odd.

Only later did I realize that John, a computer science professor at a nearby university, was working through how to create the systems architecture for one of the first–and for a time, most successful–language-learning software products.

For John and his brother-in-law Allen, Rosetta Stone was just a side hustle.

If you’ve been thinking about starting a business while keeping your full-time job and are searching for a little motivation, here are some successful companies that began as side hustles.

Instagram

While working at Nextstop, Kevin Systrom decided to create his own location-based iPhone app: one that let users check in at specific locations, make plans for future

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