The Sodipodi Hydra branch was an attempt to speed up development on Sodipodi. Sodipodi, as a project, had many issues with developers other than the lead developer getting code into the Sodipodi codebase. Many felt that this stiffled innovation within Sodipodi. In order to bring these patches and ideas of developers into the CVS tree a branch was created. This branch was named hydra-oct (Hydra as a creature that has multiple HEADS and Oct for October which was the month it was done in). This branch was largely successful in getting contributions from external developers, but had some difficulty getting into the main Sodipodi release structure (though it has been merged today). The Sodipodi Hydra branch is the basis for Inkscape on both a social and a technical level.
More information can be found at Announcement To Sodipodi.