Here is the webpage
for Umsat, a SAT-solver implementing several different constraint types. Apart
from boolean clauses in CNF these include e.g. symmetry breaking constraints and
cardinality constraints.

GrafPack, a Mathematica package for graph theory

Together with Per Håkan Lundow I have developed a Mathematica package which extendes Mathematicas standard discrete mathematics packaga in several ways. The package is maintained by Lundow and is available for download from his webpage . The webpage for GrafPack

gteditor, a graph editor in Java

this is a progam that one of my students wrote as a project in computer
science. It is a nice editor for manipulation small graphs in various
formats. The webpage of gteditor