1. Uber

Cars anytime

Founders: Travis Kalanick, Garrett Camp
Launched: 2010
Funding: $12.5 billion
Valuation: $66 billion
Disrupting: public transportation, taxi and limousine services
Rival: Lyft

Travis Kalanick, founder and CEO of Uber
Source: Uber
Travis Kalanick, founder and CEO of Uber

As it approaches its sixth birthday, Uber is finding itself in the news as much for its size and growth as for its tangles with unions and city politicians.

Read MoreFULL LIST: 2016 DISRUPTOR 50

In mid-May the San Francisco-based company that lets users hail a car with a few taps on its mobile app abruptly pulled out of Austin, Texas, after the city passed legislation that would have required the company to fingerprint its drivers. Around the same time, Uber also signed an agreement with the International Association of Machinists that puts in place a series of protections for Uber drivers in New York City, where most choose to work 35 hours or more a week. That's more than anywhere else in the country, and for that reason, New York City drivers are now going to get regular meetings with management, discounted life and disability insurance, as well as a pilot program that will require passengers pay if they keep an Uber driver waiting for more than two minutes.

Even with all these public stumbles and concessions, the company, launched by serial entrepreneurs Travis Kalanick — also CEO — and Garrett Camp is growing quickly. Before starting Uber, Kalanick had just sold his content-delivery company — Red Swoosh — to Akamai Technologies. Camp had sold StumbleUpon, his web discovery engine to eBay.

Since its founding in 2010, Uber has expanded to more than 440 cities across nearly 60 countries. It has raised a whopping $12.5 billion in equity financing from such venture heavyweights as Google Ventures and Kleiner, Perkins, Caufield and Byers. Uber is private and doesn't release financials, but industry experts have projected that its 2016 net revenues could be close to $2.5 billion.

Of course, the question on the minds of most investors is when the company will go public. CEO Kalanick has told reporters an IPO "will happen as late as possible." And why wouldn't it? He's on track to raise $10 billion in private funding without having to withstand the glare of Wall Street and the pressure-cooker of quarterly earnings reports. Maybe the better question is: Does Uber even have to go public?

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