From their site:

"I'm very pleased to announce that the Nonprofit Starter Pack is released today as an open source software project! We've heard feedback from our community of users and partners and decided opening up the code and processes around the Nonprofit Starter Pack was the way to maximize the benefit to the nonprofits we serve. In this post I'll let you know why we're open sourcing, what we hope to accomplish, and how we're going about it. I'll also be asking you to join in our effort to help nonprofits using Salesforce.com be as effective as possible."

Read more at http://blogs.salesforce.com/nonprofit/2009/06/open-s.html [1] The code is up on Google Code at http://code.google.com/p/npsp/ [2] under a new BSD license. A big "Thank you" to Chas Yen [3] for the tip.