Data.gov is powered by two open source applications, CKAN and WordPress, and it is developed publicly on GitHub. We welcome bug reports and feature requests in the project issue tracker and we highly encourage pull requests. The code behind data.gov is already publicly available, but proper releases will also be listed here once they have been packaged for more widespread use.
Software that leverages open data is also profiled on the Applications page. Most of these aren’t open source, but be sure to watch for blog posts here in the developers section for examples of relevant open source utilities for working with open data.
Beyond data.gov, the Federal Government is part of a flourishing open source ecosystem. The Government GitHub Projects page provides links to wide range of open source projects and open source community research.