Roughly speaking, with Zen (and now again with our new startup TaskTorch), I was in charge of the technical side of the business, and she was in charge of anything non-technical (finance, marketing, support, etc.)
Niki is an industrial-organizational psychologist, so her viewpoint is completely different from mine as a software engineer. As a developer it can be hard for me to see past the software sometimes, and Niki's perspective helps quite a bit.