Boston, one of America's oldest cities, has a well-earned reputation for higher education, culture, and history-making tea parties. What's not as widely known, though, is that the city also is a hotbed of fast-growing businesses. This year, 33 Olde Towne companies made the Inc. 5000 list. Here are the top 10--six of which are holdovers from last year's list--ranked by their revenue growth over the past three years.

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10. Apptopia

2018 Inc. 5000 rank No. 1320 Three-year growth 363% 2017 revenue $2.8M

Apptopia provides such customers as Uber, Facebook, and Google with useful metrics and insights about their mobile apps. The company's investors include billionaire entrepreneur Mark Cuban, as well as Expansion Venture Capital and 500 Startups.

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9. The CERES Group

2018 Inc. 5000 rank No. 1140 Three-year growth 431% 2017 revenue $4.5M

With an emphasis on long-term placement, The CERES Group is an IT staffing firm that's making its second appearance in a row on the Inc. 5000 list. The business, which has maintained its rapid growth despite a staff of just six people, also trains U.S. military veterans to become talent recruiters through an initiative called The McNeil Project.

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8. Bay State Search

2018 Inc. 5000 rank No. 1098 Three-year growth 449% 2017 revenue $13M

Two-time Inc.5000 honoree Bay State Search is a staffing firm that specializes in accounting and finance, IT, customer service, legal services, and administration. In addition to being among the top Boston businesses on the Inc. 5000, it is also one of the 20 fastest-growing human resources companies.

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7. Pixability

2018 Inc. 5000 rank No. 934 Three-year growth 530% 2017 revenue $27.9M

Pixability provides a platform for purchasing ads on video streaming sites. The company maintains a presence far beyond Boston with offices in New York City, Chicago, San Francisco, and London, and this year is making its third appearance on the Inc. 5000 list. 

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6. WordStream

2018 Inc. 5000 rank No. 924 Three-year growth 535% 2017 revenue $47.3M

Making its sixth consecutive appearance on the Inc. 5000 list, WordStream, a marketing software company that helps clients optimize online advertising, has come far from its roots. The founders came up with the idea in a Panera Bread restaurant, and the company now has more than 220 employees and offices in Boston's tony Back Bay neighborhood.

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5. Biena Snacks

2018 Inc. 5000 rank No. 615 Three-year growth 815% 2017 revenue $4.8M

Biena Snacks got its start when its founder, Poorvi Patodia, started making chickpea snacks as a healthy between-meals food option during her pregnancy. Now, the snacks are sold in Whole Foods stores and feature flavors ranging from barbeque to Girls Scouts' Thin Mints.

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4. Audley Travel US

2018 Inc. 5000 rank No. 513 Three-year growth 980% 2017 revenue $62.4M

Located in Boston's historic North End, Audley Travel US offers customized vacation and travel plans to a variety of locations around the world. The company got its start in 1991, when co-founder Craig Burkinshaw led small group tours around Vietnam after graduating from college. Today, Audley Travel US offers trips on every continent. 

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3. Forward Financing

2018 Inc. 5000 rank No. 404 Three-year growth 1,238% 2017 revenue $42.1M

Two-time Inc. 5000 honoree Forward Financing provides working capital and financial services to small and midsize businesses. Since it opened its doors in 2012, the company has funded more than $300 million for over 9,000 customers. 

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2. Social Fulcrum

2018 Inc. 5000 rank No. 384 Three-year growth 1,276% 2017 revenue $8.7M

Social Fulcrum is an advertising agency that focuses on Facebook and Instagram campaigns. Co-founder and CEO Andrew Krebs-Smith started three other companies prior to Social Fulcrum, which is on the Inc. 5000 list for the second year in a row.

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1. 2020 On-site

2018 Inc. 5000 rank No. 211 Three-year growth 2,175% 2017 revenue $2.6M

The fastest-growing private company in Boston this year, 2020 On-site  drives RVs-turned-eye-clinics right to companies' doors for fast eye doctor appointments. The business has seen more than 30,000 patients since its 2013 founding, and it's an official partner with Boston Public Schools.