Proposals are created using a number of different content blocks, ranging from general text blocks and costing tables to sitemaps and assets. Proposals are accessible only by the author and the users associated with the entry.
Discovery documents have a set number of questions that help a potential client think about the requirements for their project. This base set of questions can be added to on a client-by-client basis if more specific content is required.
Briefs are documents created by the client. Using a front-end interface that saves entries back into Craft, the client is able to specify what that need from a specific brief and have that information saved into an updatable entry in Craft, only accessible by the client and Designfront.
Guides are generally used to put together information about client websites and are good reference when more involved tasks require a more detailed explanation.