This is ns-3-allinone.

If you have downloaded this in tarball release format, this directory
contains some released ns-3 version, along with 3rd party components
necessary to support all optional ns-3 features, such as Python
bindings and Network Simulation Cradle.  In this case, just run the
script build.py; all the components, plus ns-3 itself, will thus be
built.

If, on the other hand, you have obtained this by cloning the mercurial
repository, this directory only contains a few python scripts:

  download.py:
   
     This script will take care of downloading all necessary
     components, including pybindgen and NSC, along with cloning an
     ns-3 repository.  By default, the main development ns-3 branch,
     ns-3-dev, will be cloned, but it can be overridden via the -n
     command line option.  For example,
     
       ./download.py -n craigdo/ns-3-tap

     will clone the repository http://code.nsnam.org/craigdo/ns-3-tap
     into the allinone directory.

     By default, regression traces will not be downloaded.  You can
     override this using the -r command line option.  For example,

       ./download.py -n craigdo/ns-3-tap -r craigdo/ns-3-tap-ref-traces

     will clone the repository http://code.nsnam.org/craigdo/ns-3-tap
     into the allinone directory and also clone the reference traces
     from the http://code.nsnam.org/craigdo/ns-3-tap-ref-traces repo.
     Note that regression traces are only available for ns-3 releases
     up to version ns-3.9.

  build.py:

     This script will get all external components that need to be
     built, and then will build ns-3 using the downloaded components.