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