> You duplicate data every time you send an Excel file by email
As much as I hate Sharepoint, it's actually, as of this year, come close to solving this problem. Full fledged Excel (and Word) documents synced between many authors working simultaneously (section-wise edit locks until next explicit save/sync), no one ever emails anything around. It's not all the way to a Git-like solution, and (at least for the moment) tied to IE on Windows, but compared to the old ways, it's a winner.
As much as I hate Sharepoint, it's actually, as of this year, come close to solving this problem. Full fledged Excel (and Word) documents synced between many authors working simultaneously (section-wise edit locks until next explicit save/sync), no one ever emails anything around. It's not all the way to a Git-like solution, and (at least for the moment) tied to IE on Windows, but compared to the old ways, it's a winner.