Google Drive is Google's file sync app that lets you store all of your files online alongside your Google Docs documents, and keep them synced with all of your devices.
Put the creative brief beside work awaiting your approval.
Your reviewers see the brief beside the asset, with the brand decision they need to make clearly stated.
Put the current creative draft in each task awaiting sign-off.
Your brand reviewer gets the current campaign draft and the decision needed together on the review task.