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Gitblit is available for Windows, OS X and Linux.
Pro Just works
Setting up is easy and usage is intuitive.
Pro Free and open source
GitBlit is free and open source (under Apache License) .
Pro Built-in authorization in windows
So you don't have to worry about setting up OpenSSH on Windows.
Con No project admins
There's no separation between a system admin and a project admin. There's owners for projects, but to create a new repository one has to be a general admin.
Con Access controls are repository-based
Built in access controls are not branch-based.