What tool is this - or anyone got an alternative tool

Question

I need to make a very simple drawing of a graph (NOT a chart but a graph, like in Dijkstra) with multiple nodes and multiple vertexes.

I once saw this guy using a tool where he wrote the data in notepad then compiled or something and then he had an svg to view in a browser - to me this should be the simplest tool to draw this graph in. Anyone know what this tool is? Or know a simple, open source/free tool to make simple graphes (need to be able to automatically rearrange it so it looks decent)

Cheers,

Answer 1

Try Graphviz:

http://www.graphviz.org/

Answer 2

http://granite.sru.edu/dailey09/grapher.html