C.a.R.– Compass and Ruler (also known as Z.u.L., which stands for the German "Zirkel und Lineal") — is a free and open source interactive geometry software that can do geometrical constructions in Euclidean and non-Euclidean geometry. The software is Java based. The author is Rene Grothmann of the Catholic University of Eichstätt-Ingolstadt.It is licensed under the terms of the GNU General Public License (GPL).