We tend to keep ours on Sharepoint - which means we could use Excel Online to work collaboratively, but usually we don't need them all at the same time, so open

We tend to keep ours on Sharepoint - which means we could use Excel Online to work collaboratively, but usually we don't need them all at the same time, so open in Excel desktop and "check it out". If someone else needs it, they can just ping on Skype and see if you're done.