You can use GIMP to open and edit EPS files created by Abode Illustrator.

In previous versions this required installing Ghostscript and setting up a system environment variable used by GIMP to locate the Ghostscript executable.

GIMP now bundles the Ghostscript library with the GIMP installation, so the above isn’t necessary. However, it appears something’s awry with the the DLL file included with the GIMP installation – so that importing a postscript file into GIMP gives a “could not interpret Postscript file” error – so you need to replace the bundled DLL with the functional Ghostscript DLL.

The above was learned after much googling and link following and trial and error, which was finally put to rest with the instructions here.