Clawpack development is done using Git <http://git-scm.com/> for version control.
There is an overarching Clawpack “Organization” on Github located at https://github.com/clawpack. Under this, there are now several separate repositories for moving forward with Clawpack development.
The 4.x line of Clawpack is in the repository clawpack-4.x.
If you want the latest version of Clawpack 4.x, you can clone this repository:
$ git clone git://github.com/clawpack/clawpack-4.x.git /path/to/local/clawpack-4.x
With luck, Clawpack 4.x will soon be obsolete since work is well underway to upgrade to Clawpack 5.0.
For Clawpack 5.0 and beyond, there are separate repositories for each major piece of Clawpack: classic, amrclaw, geoclaw, visclaw, util, etc.
See https://github.com/clawpack/doc/wiki for more about this, and about plans for other changes.