XtalView is a molecular graphics program that I wrote some years ago for protein crystallography based on xview and X11. It is unsupported these days but I still have some downloads available:
XtalView for Darwin (Mac OSX) - You will need to know a bit about Unix to get this working. I had to rename this file as .mp3 to get around my network providers file limits. After saving the file, change the .mp3 extension to .Z. Use uncompress from the command line to turn into a tar file. Then use tar to install.