This question indicates you should have no problems having a central Mercurial repository on a network share, given certain limitations: Can you ‘push’ to network share using Mercurial on 64bit Windows 7?
However, individual users will still have local copies of the repository.
Before ruling out non-shared folder methods, you should review Mercurial’s page on publishing repositories. Also, look about halfway down on this Git page (specifically, the “Distributed” section). What you want should work with both Mercurial and Git, but it’s not how people tend to use these version control systems.
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solved Free source control tool to replace CVS – separate repository /working folders are required [closed]