Font families can sell for hundreds of dollars. Gotham, a popular typeface used by President Barack Obama’s campaign and many others, costs nearly $1,000 to license a complete set of 66 different styles. But The League of Moveable Type, gives all of its fonts away for free. What's more, it makes them open source, so that other people can modify the fonts and make their own versions of them.

And people have. Raleway, designed by Matt McInerney and released in 2010, was expanded from a single weight into a family with nine weights, from “thin” to bold to “black,” each with matching italics, in 2012 by Pablo Impallari, Rodrigo Fuenzalida, and Igino Marini. It's now one of the most popular font families on Google Fonts, a collection of free fonts hosted by the search giant.

Over the past decade, companies ranging from startups like the IT tool company Datto to giants like Intel and IBM have commissioned professional type makers to create fonts that those companies open sourced. Even Adobe, which sells licenses for some of its font families for hundreds of dollars, has released a "super family" of open source fonts.

It's easy to see why web designers would want free, high-quality fonts. But why would an independent type designer open source their work? Just as in open source software, the reasons vary.

For companies, the reasons to open source a font that they've commissioned often mirror the motivations for releasing open source software. For example, programming tool maker JetBrains released a new font called JetBrains Mono designed for reading and writing code. The company open sourced the font so that programmers could easily provide feedback and improvements through Microsoft's code hosting and collaboration platform GitHub, much as a company might release open source software in the hope that others will help improve it. "It feels like a real collaboration," says JetBrains team lead Konstantin Bulenkov.

Even if designers don't contribute improvements to a font directly, companies can benefit from making their work open source. For example, Adobe Type senior manager Dan Rhatigan says releasing its Source super-family of fonts as open source has enabled the company to test new typography technologies like "variable fonts," which make it easy for a designer to adjust the weight of a typeface, before rolling those technologies into other products.

In other cases, open source fonts help support other aspects of a company's business. For example, Google Fonts program manager Dave Crossland says many of the fonts Google has funded most recently are designed for under-supported languages in developing countries. These efforts buttress Google's "Next Billion Users" initiative, which aims to bring more people in developing countries online. Better support for more languages means more users, and ultimately, more money for Google.

The incentives to create open source fonts weren't always obvious. In early 2009, a graphic designer and programmer named Micah Rich came across a forum post by a student who was interested in knowing more about how fonts worked. The student asked whether there was a professional-quality open source font to learn from. The replies weren't kind. "There were like 20 pages of professional type designers saying, 'This is our livelihood, how dare you ask us to work for free?'" Rich says.

Rich understood where the designers were coming from. Type design is a laborious craft. In addition to drawing hundreds or thousands of individual characters, you need to define the relationship between characters or groups of characters. It takes months of full-time work to create a new font. But the complete dismissal of the open source model bugged him.