The binary packages for GSL Shell are provided for Windows only. The debian packages are no longer provided. You are encouraged to compile GSL Shell from the source code or otherwise ask to the maintainers of your favorite distribution to include a package for GSL Shell.
To use the windows binaries just unzip the archive is a folder of your choice. To start GSL Shell you need to double click on the executable.
GSL Shell is free software and its source code is available:
All the older releases can be found in the download area, hosted at Savannah.
You can create a local copy of the git repository using the following command:
git clone git://github.com/franko/gsl-shell.git
Another git repository is hosted at Savannah. You can find it in the Savannah's project page but it is recommended to use the Github's repository.