How can I open (or convert into .PGN) old Chessmaster .CMG files, without Chessmaster? I have many old chess games saved from Chessmaster 7000, 8000, and maybe even 9000. They are all saved in the Chessmaster .CMG file format.

How can I access these games today?

I would like to either open them or convert them to .PGN format.
To access them today, you either need to reverse engineer the format (hard) or export them to PGN inside Chessmaster (moderate):


  HOW TO CONVERT CHESSMASTER GAME FILES (*.CMG) TO *.PGN FILES
  
  (*.CMG files or Chessmaster game files are typically for use with the
  Chessmaster programs and may contain various enhancements, such as
  annotations, illustrated voice analyses, etc. Cf. page 25 of the
  Chessmaster 9000 user manual.)
  
  
  Log in (on Chessmaster 9000) and go to Game Room.
  Click on "File" in upper menu bar and then on "Load" in pull- down menu, to get "File Open" window.
  By default, the "Look in" box will show a folder that is named the same as the name you log in with. Let's say it is "Loginame." If the
  file you wish to convert is not in the list in the big box below, then
  you will have to find it by scrolling to other folders. In front of
  the file the little icon will contain the number 9000. (The icons for
  *.PGN files contain the initials PGN.)
  Click on the name of the *.CMG file that you wish to convert. The name will show in the "File name" box below. The "File of type" box
  should mention Chessmaster files. Leave "Auto" in the last ("Open as")
  box. Click the "Load" button and get the game on the board.
  Click on "File" and then on "Save" in the pull-down menu.
  "File Save" window comes up next. Check that the "Save in" folder is acceptable. (Your "Loginame" folder is OK, but you could even
  scroll to save the file on the floppy in drive a:) In the "File name"
  box below you can fill in a shorter (8-character) name of your choice,
  rather than accepting the long name created by Windows. In the "Save
  as type" box at the bottom,scroll and pick "PGN Game Files (*.PGN).
  Click on the "Save" button. In the "Annotation Type" window that comes
  up next, accept "None" by clicking "OK."
  The *.CMG file has been stripped to the plain *.PGN format and saved in the folder that you have chosen. If you wish to add this file
  to a database of your choice, see our earlier instructions under the
  appropriate heading.
  


Obviously, if you don't have Chessmaster installed, you will need to do that.  Easiest way might be to install a Windows VM, then install a legacy copy of Chessmaster.