Open file without Adobe Illustrator

Inkscape

It may not open CC version of Illustrator, I think it will take up to version 8.

..I personally use a few ways,  Rhino3D and Inkscape and the rename to pdf,.. although, it depends..  do a search and you may find something which suits your needs,... 

https://www.google.com/#q=free+software++open+.ai+file++Adobe+Illustrator

https://www.credera.com/blog/technology-insights/viewing-and-working-with-ai-files-vector-art-without-adobe-illustrator/

Illustrator Recovery Toolbox will restore and convert an .AI file so you can view. There is a demo version so you can check the tool whether it will be useful to you or not. http://www.oemailrecovery.com/illustrator_recovery.html

I don't use AI here, but I have some sample AI files for testing purposes, and Illustrator Recovery Toolbox can open them. As with most things Adobe, AI is a complex format, so don't be surprised that they can open some AI files and not others. At the end of the day, AI is an Adobe proprietary format, so I suspect the only total support is from Adobe itself. Wikipedia has a list programs that support AI files, which, in the free arena, contains Ghostscript and XnView (via Ghostscript), so I guess they represent other free possibilities for sglee, although I haven't tried them (btw, that may be why IrfanView works — it utilizes Ghostscript, too — although neither IrfanView nor GIMP is on the Wikipedia list).

If you have Acrobat Reader, just rename the files from *.ai to *.pdf to view them.