How do you open ai. files without buying Adobe Illustrator?

I have a number of technical drawings drawn in ai format (Illustrator CS2) left over from a 2007 project and I can view (read-only) them at least three ways without Illustrator:

1) Use Quickview. Highlight the desired file and press the SPACE bar

2) I just confirmed Preview works.

3) Adobe Reader will open it.

Editing may not be possible without Illustrator. Right-clicking to see "Open with..." on of my .ai file shows two other installed programs will open the files. I have PhotoShop Elements 12 as one option. I just tried importing an .ai into PSE and it converts it to a pdf on the fly before presenting on-screen, so editing is probably nit possible.

I also bought Affinity Designer, which is an Illustrator replacement that is affordable. The latter is in the App Store for a "doable" price of US$50 here:

https://itunes.apple.com/us/app/affinity-designer/id824171161?mt=12

Unfortunately it also treats the file as an imported pdf and, and as the file was grouped and flattened in Illustrator, Designer's "ungroup" command is greyed out so I can't edit. Success in editing may totally depend on how the file was treated in Illustrator when it was created.

Still one gets a nice view by most of these methods, although PSE uses Adobe's grey/with checkerboard pattern to denote the transparent background--a tad ugly.

Programs that can do that are listed at http://fileinfo.com/extension/ai

It claim that they can be opened by Preview.