DDS spun out of US Digital Service and DDS members go through the USDS hiring pipeline.

18F, USDS, and the Presidential Innovation Fellowships are philosophically related, but organizationally and functionally distinct.

The Defense Digital Service and the US Digital Service are distinct organizations: http://www.defenseone.com/technology/2015/11/meet-head-penta...

I'm from 18F, and I'm now a "contributor", but only because they accepted my pull requests. :)