IndieBound.org is made of Drupal, an open-source web framework based on PHP. It is database-agnostic, which does NOT mean that it doesn't believe in databases—oh no, Drupal believes in databases, some would say too strongly—but it can interface with (potentially) any database through a key innovation called a database abstraction layer.
One of the greatest things about Drupal is its extensibility through user-contributed modules. Modules extend the functionality of Drupal without interfering with its core code. This means they tend to play nicely together. For example, points—the scores that appear next to users' names—are an implementation of a Drupal module called (surprise!) userpoints. Your "favorite stores" and your "friends list" are done with implementations of Drupal modules (flag and buddy_api, respectively) Modules are easy to implement out of the box, but tweaking them to work just the way you want them to can be tricky.
The best thing (from a developer's point of view) about using Drupal is the vast user community that supports it. Because Drupal is open source, you can go to drupal.org and listen in on developers' conversations as the framework matures. It's a great way to find out why things were done a certain way, or to learn how most users get around a certain quirk of the core Drupal framework. And not only on Drupal.org, but on private websites and blogs (like this one), Drupal users/admins post all kinds of tutorials, how-tos, etc. A little Google-assisted research was usually all I needed to find the answers to problems I was having as I worked on this community site.
One of my favorite parts of the Drupal website is the Drupal Showcase, where developers discuss how they adapted Drupal to make their own websites. (See, for example, The New York Observer.) Once the dust settles from launching this community, I intend to add one, too.
The more I learn about the Drupal framework, the more I come to realize how perfect a match it is for the IndieBound movement. Drupal, like a lot of open source software, is supported by an immense community of interested users at all skill levels, sharing advice, tips, complaints, wish lists, and aspirations, and all of them committed to the same values—creativity, openness, and Doing It Yourself. And ultimately, that's what I'd like to see IndieBound.org become the nexus for—a vibrant community, online and offline, of individuals dedicated to independence and living local.