The sell is that my manager can send an Excel spreadsheet to everyone and everyone can open the spreadsheet and edit it at the same times while seeing everyone else do their edits. What's the non-MS non-Google solution to this?

Open-Xchange supports collaborative editing of spreadsheets. Mailbox.org uses that for their email service, and you get access to their online office suite when you subscribe. I can't speak to the quality of the shared editing, but their online office suite is fine for basic stuff.

Anyone can edit it and it also might get randomly corrupted. It’s crap, especially if some people are on Macs.

Zoho.