Gavrog stands for "Generation, Analysis and Visualization of Reticular Ornaments using Gavrog". It is a Java library together with a suite of interactive applications for the study of periodic net-like structures in space and their applications.
The program fuses 2 sets of molecules. It tries different relative positions of molecules before binding them, so that there is no or minimal intersection in the resulting molecule. The atom to be fused in a molecule is labeled with an R symbol.