I do not have excel in any version and I’d rather not use Google docs, so was wondering if I could use a different software spreadsheet. I couldn’t find any obvious solution and it seemed that it wouldn’t matter.
No, the add-ins required are currently only available for Google Docs and Excel.
It seems, with 497 Views, this might be a good feature request. I, for one, would vote for it. @bpesvcs have you opened one? I can add my name to it. Also willing to beta test and or help out on implementation if you want to make it a open source bridge addon. 
Like the username, @privacyMatters. I’m bumping this over to the Feature Requests category.
BTW… when this was posted, our Excel offering wasn’t as mature. Now, many users with privacy concerns regarding Google are using Excel. Is that possibly a solution for you?