Developer tools
Threepress endorses free, open source software and wherever possible strives to make source code available. All public Threepress code is licensed under the BSD license, which allows for unrestricted commercial or non-commercial use.
ePub validator
Upload a DRM-free ePub document to validate it against the schemas
supplied with the Adobe epubcheck tool.
ePub tools
Hosted on Google Code, epub-tools are Python libraries for converting from TEI and DocBook into ePub. These tools have been used by individuals in ePub-generating projects and have been incorporated into the Calibre ebook conversion suite. Additional contributions from Adobe.
Bookworm
Although primarily a web platform for use by readers of the ePub file format, the majority of Bookworm code is released as open source. Developers are encouraged to reuse code, tests or sample data in developing their own ePub applications. Source code hosted on Google Code, site hosting provided by O'Reilly Media.
Threepress blog
The Threepress blog contains hundreds of archived and recent posts about the ePub standard, ebook development and other items of interest to digital publishing.