Graphviz
Graphviz is a popular tool to generate graphs.
$ sudo apt-get install graphviz
$ dot -c # once, initialize graphviz
A short complete example:
digraph {
size="10,8";
rankdir="LR";
"Bourse" -> "OpΓ©ra" [ label="5" ];
a [style=filled,color=red];
a -> b [arrowhead = none];
d -> k;
}