Chef, the company, has a few tools besides Chef in their tool suite. Habitat is a tool created to help with the automation of applications and their deployment.
One of the issues with deploying applications is that we often manage the steps separately using different tools and we need to change how we do things based on the deployment target. Habitat aims to consolidate how we think about deploying our applications and also allow us to deploy "any app, anywhere". Everything that an application needs to be deployed is moved into the application itself in the form of a "plan", including secret management, runtime dependencies, build dependencies, and the process for deploying the application.