If you want to compile the project or to modify it you can download the last version of the LibrePlan source code at https://github.com/LibrePlan/libreplan. Have a look at the HACKING.rst file for instructions on how to compile.
Another option is download LibrePlan by cloning the git repository and start playing:
git clone git://github.com/LibrePlan/libreplan.git
Finally, if you wish to have a look at the git repository browsing it on-line, you can do it at:
Additonal useful information about compilation and hacking can be found in the wiki pages on GitHub.