ShipIt is a Google Docs extension that makes it easy to formalize the document review process.  It streamlines the collection of feedback from multiple users, keeps interested users up-to-date on the state of the document and enhances collaboration between multiple authors.

It has the following features:

Author Management:
Document owners can add authors to the document giving them the ability to modify the document and obtain and respond to feedback left by reviewers.

Reviewer Management:
Authors can add and delete reviewers to the document, remind them to review the document and disseminate changes to reviewers as they are done.

Reviews:
Reviewers can leave feedback on a document and approve or request changes to documents.

Document staging and Issue:
Authors can move a document through the draft, and review stage, issue new versions of a document and deprecate older versions of a document. 

Notifications:
Authors and reviewers can watch a document and be notified of changes in its content or state, discussion and reviews on the document and when a new version of the document is issued.

Labels:
Authors can tag a document with a set of free-form labels. Both authors and users can search against these labels in Google Drive.