Amazon has made a rare investment in Acquia, a Burlington, Mass.-based digital marketing company that operates on Amazon’s cloud services.

The undisclosed investment piggybacks on a $50 million round closed in May from major investors, including Sigma Partners and New Enterprise Associates. In all, the company has raised more than $100 million over several rounds of funding.

The company said the money will be used to help deliver an open cloud platform for content, community and commerce.

Investments made directly by Amazon, and not Jeff Bezos, are fairly infrequent. Recent examples include small investments in e-commerce companies in China or India. Perhaps, domestically, the biggest largest example is an equity stake it took in Washington, D.C.-based LivingSocial. (Another investment was made today into security app Lookout, but it was by Bezos Expeditions, the personal investment fund of Amazon’s CEO, and not the company).

This one is slightly different because Acquia is not consumer-facing. It operates on Amazon’s Web Services.

“We are pleased to help further the development of Acquia’s digital engagement solutions,” said Jeff Blackburn, Amazon’s SVP of business development, in a statement. “Acquia on AWS helps organizations of all sizes leverage cloud computing to power fast and reliable digital experiences at scale.”

Acquia refers to itself as “a digital business company” that works with companies, including Pinterest, Mercedes Benz, Warner Music Group and Stanford University. According to a release, these companies rely on Acquia to generate new revenue, lower costs, and engage audiences by using content, community, commerce and context.

In an example, it said it helped Timex create a shopping experience that consumers have grown to expect from brands. The purchasing experienced targeted athletes and included fitness-related articles, product information and reviews.