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.