Is there Molecular Origami for a Mac?

Molecular Origami is not available for the Macintosh. Sorry, but there are no plans to come out with a Mac version.
Even though you cannot use the program Molecular Origami, you can still print over 250 structures. Just follow the instructions below, and when you need files go to the FTP site.

Excerpted from the file - readme.1st

You will need a Macintosh with an attached Apple Laser Writer 
or other PostScript device.

Ensure that that printer is chosen using Chooser.
You will also need the LaserWriter Font Utility program.
Use the one that came with your system. (You may not
have loaded it from one of the utility diskettes.)

1. Copy the origami directory to your hard disk.
2. Open your LaserWriter Font Utility
3. Under Utilities in the LaserWriter Font Utility program, 
   select "Download Postscript file..."

                        Select   ORIGAMI.MAC   

    This is the main dictionary file.  It must be sent ONCE 
    each time the printer is turned on. The program will 
    offer to save a log of the session. Allow it to 
    overwrite any previous log file.

4. Send whichever sample file you would like the same way.

Feel free to open these ASCII files with TeachText or 
Word and change them in whatever way seems appropriate. 
The worst that can happen is that the page will not print.
You can check the log file for details as to why a 
structure might not have printed. 

ORIGAMI.TSTMAC, when sent to the printer, should produce a single 
page, CH4.