In 2012 Loic Le Coq (the author of xlogo) made a Qt front end for giac and called it qcas.
The Qcas forum is located on xcas site. Since 2013 I have made some modifications and binaries. For More details look at the git repository of Qcas. In particular, qcas can now use the same giac library as xcas, so the speed and functionalities are similar except that 3D is not yet implemented.
This interface is also avaible from giacpy to display giac graphics from python.