It is slightly modified off the 6pac SlickGrid repo with some specific improvements.
Check out the NEW SlickGrid Website! http://slickgrid.net/
This is the acknowledged most active non-customised fork of SlickGrid.
It aims to be a viable alternative master repo, building on the legacy of the mleibman/SlickGrid master branch, keeping libraries up to date and applying small, safe core patches and enhancements without turning into a personalised build.
Check out the examples for examples demonstrating new features and use cases, such as dynamic grid creation and editors with third party controls.
Also check out the wiki for news and documentation.