WorkStrip for Mac

From Softchaos:

WorkStrip is an intelligent, system wide productivity enhancement tool for professional and intensive Mac users. Floating above the desktop, WorkStrip provides a host of intuitive features:

• Multiple Workspaces to organize your work
  
• Instant file previews without loading an application
  
• Advanced tracking of applications, documents & web sites
  
• Bookmarked favorite items for ease of access
  
• Instant panel views of recent files, folders and bookmarks
  
• Navigate your important files and folders without switching back to the Finder
  
• Instant access to all your document windows, across all applications*
  
• Keep track of the documents you are using on a per-project (workspace) basis*
  (* requires Mac OS X 10.2.4 or later)