Developer platform Xamarin, which powers apps like Rdio and Tom Hanks’ mega-popular typewriter app, today announced a massive $54.25 million to fuel its expansion into Europe.

Xamarin enables developers to build native apps for iOS, Android, Windows, and Mac, in one programming language. The C# language, to be specific. According to Zamarin chief Nat Friedman, C#’s developer community numbers in the millions, and for those developers, Xamarin’s code-sharing platform is apparently a godsend.

The company touts “tens of thousands of customers” and 200 employees since launching three years ago. According to Friedman, this is “the largest round raised by a mobile platform company ever.”

Xamarin certainly has big names behind it. Aside from Rdio, its customers include Microsoft, GitHub, Nielsen, and Kellogg’s.

But don’t compare the company to write once, run anywhere platforms. In a call with VentureBeat, Friedman insisted that Xamarin is far different from services like PhoneGap, which enables developers to package Web apps as native apps. “We do not support write once run anywhere. We think by definition it results in a mediocre experience.”

“We’re saying share code. We’re not saying write once run anywhere.”

With new capital in hand, Friedman says Xamarin’s financing will be used for expansion, primarily in Europe. “We don’t have any sales or marketing on the ground there,” Friedman tells us. “We’re opening this fall in London … we might use some of the proceeds to potentially do some M&A. We’ve already acquired two companies in the last year or so.”

To date, Xamarin has raised $82 million in funding. The company is based in San Francisco.