Archive of electronic documents

Greetings to you Habrosocommunity.

Not so long ago, the bosses at the company set the puzzle:
“Find a system that will allow you to organize a convenient archive of electronic documents ”

System Requirement:

• Electronic Document Storage
• The ability to tag documents
• Multiuse
• Cross-platform (Windows, MacOS, Linux)
• Distribution of documents by "topics"
• The possibility of organizing a single (preferably tree) structure "themes"
• Editing documents in an external editor with an automatic backload apload
• Differentiation of access rights
• Search (by tags, by dates of creation and change)
• System availability 24/7

Several hours of fermentation in Google did not give any result, so I decided to turn to more experienced habroles for advice.
Who faced with such systems, do not remain indifferent.