I think Joey Hess' attempt at "solving the problem" deserves a mention.
It is open source (GPLV3) licensed. [not proprietary]
Written in Haskell. [cool aid]
Currently has 1200+ stars on Github and is part of at least Ubuntu (http://packages.ubuntu.com/search?keywords=git-annex) since 12.04. [shows something for support and adoption]
edit: Link to Github https://github.com/joeyh/git-annex -- thanks dgellow