This project uses Git to manage its source code. Instructions on Git use can be found at https://git-scm.com/documentation.
The source can be checked out anonymously from Git with this command (See https://git-scm.com/docs/git-clone):
$ git clone https://gitlab.orekit.org/orekit/orekit.git
Only project developers can access the Git tree via this method (See https://git-scm.com/docs/git-clone).
$ git clone ssh://git@gitlab.orekit.org/orekit/orekit.git