file sharing, document collaboration software or library

I am trying to integrate file sharing functional开发者_StackOverflow社区ity to existing web portal. Do you know any software or library which can help me? It must be collaboration tool, employees should be able to manage and edit for example project files, add comments to that files. It is similar to SharePoint software.

Opensource and proprietary software are acceptable.

Any ideas?

google documents does this well.

Samepage.io was originally built as an on-premise server software platform, but it has moved to the cloud. I use it every day to collaborate with both internal and external teams. It offers everything you might expect in terms of file sharing, document collaboration, task management, comments, etc. It also integrates with Google Drive, Dropbox, Box, and OneDrive for file sharing.