collaboration tool but not sharpoint

Hi Experts

i am searching for some sort of tool or way to give around 20 users possibility to work on shared directory which include MS office files

like word excel etc

we have multi shared file systems  and in one of these file shared file system we have one directory which include excel and word files

so some users want to access this off line then when they jion our network they want to sync

the problem is some time 10 users work on one file

any idea

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For simple collaboration you can just share document:
On the Review tab, in the Changes group, click Share Workbook.
In the Share Workbook dialog box, on the Editing tab, select the Allow changes by more than one user at the same time. ...

To co-author with others, you need:    
A shared storage area   OneDrive, OneDrive for Business, SharePoint Online, or a SharePoint Server document library to store your files. For real-time co-authoring, you must use the online versions, but regular co-authoring works fine with on premise SharePoint Server.

Apps that support co-authoring   Word and PowerPoint on all platforms, and on all versions since Office 2010, Excel Online, Android, and Windows Mobile. In addition, real-time co-authoring is supported on Word for Windows Desktop 2016, and Word, PowerPoint, and Excel Online.

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Rob HensonFinance AnalystCommented:
Shared Workbook feature is notoriously unreliable and can cause some serious problems in the shared files; corrupted data, file size bloat to name but two.

Shared Workbook also disables a number of features, pivot tables being one.
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