Medical device company Penumbra first turned a profit in 2012, but co-founders Adam Elsesser and Arani Bose waited until 2015 to take their company public, when they knew they had a solid portfolio of products. "We did that very much on purpose, to ensure that the foundation that we had built at the company, not just financially, but culturally, was very strong," Elsesser told Inc. The company currently designs and manufactures medical devices to treat a variety of illnesses, primarily neurovascular diseases and blood clots, and plans to add new products for at least the next decade. But Penumbra's competitors--Boston Scientific and Medtronic, to name a couple--have well-financed research divisions. This could prove challenging to Penumbra's history of innovation. Note: employee count as of Dec. 31, 2015

Ajay Mishra and Suresh Batchu founded MobileIron to modernize corporate IT systems through a mobile device management platform. MobileIron's software pledges to keep company information secure, while allowing employees to access company apps or databases on their phones, tablets, or other devices. The company also has features that allow IT departments to create their own apps, and for users to request IT assistance through their phones. The company has struggled to stay out of the red since its inception, but MobileIron expects demand for its products to grow, as mobile becomes the platform of choice for more consumers. Note: employee count as of Dec. 31, 2015

Imprivata, founded by David Ting, is helping business ditch user names and passwords. The company provides its enterprise-level customers with a variety of single sign-on methods--such as fingerprint analysis and smart identification cards--that employees can subsequently use to access various databases more quickly. Imprivata maintains that its authentication technology is secure, but could take a hit if any of its business customers were to experience a security breach. The security company's customers are primarily health care organizations, but Imprivata also works with banks, energy companies, and government organizations, and is exploring other highly regulated industries that it can service in the future. Note: employee count as of Dec. 31, 2015

Founded in 2007, Rubicon Project is one of the world’s largest advertising exchanges. The company helps websites and apps thrive by giving them tools and expertise to sell ads easily and safely. In addition, the world's leading agencies and brands rely on Rubicon Project’s technology to execute billions of advertising transactions each month. Rubicon Project is an independent, publicly traded company (NYSE:RUBI) headquartered in Los Angeles, California

Steven Boal founded Coupons.com to turn the tradition of scouring newspapers for coupons into a more high-tech process. Today, Coupons.com (now known as Quotient) acts as a digital bargain hunter for consumers, while simultaneously working with brands and retailers to provide them with insights into shoppers' habits. Boal told Inc. that the decision to rebrand Coupons.com as Quotient reflects a stronger focus on analytics, and was done to keep up with changing customer demands. "We've rebranded several times as our business has evolved," he says. Time will tell if the rebrand is a successful one. Note: employee count as of Dec. 31, 2015