Here is the link for downloading GAMBIT: 
http://www.hepforge.org/archive/gambit/gambit-1.0.1.tar.gz

In the README.md file there is a list of other packages that are needed 
to install and run GAMBIT. I've pasted the list below for convenience. 
It's mostly standard packages, but I suspect not everyone will have will 
have packages like Eigen, yaml and hdf5 installed.

-------------------

GAMBIT is built using the CMake system. The following libraries and 
packages must be installed prior to configuration:

COMPULSORY:

  - gcc/gfortran 4.7.1 or greater, or icc/ifort 12.1.0 or greater
  - Python 2.7 or greater (Python 3 is not supported)
  - Python modules: yaml, os, re, datetime, sys, getopt, shutil and 
itertools.
  - Boost 1.41 or greater
  - GNU Scientific Library (GSL) 1.10 or greater
  - Eigen 3.1.0 or greater
  - LAPACK
  - PKG Config

OPTIONAL:

  - the h5py python module (for use of the hdf5 printer)
  - MPI (required for parallel sampling)
  - axel (speeds up downloads of backends and scanners)
  - graphviz (required for model hierarchy and dependency tree plots)
  - HDF5 (for use of the hdf5 printer)
  - ROOT (required for the Delphes detector simulation, or the GreAT 
scanner from ScannerBit)