I am have been meaning to do a screencast of the Auto Optimization feature in Avogadro for a while. Fortunately Geoff Hutchison beat me to it, as you can see above, and did a much better job than I could have.
To prove that point I made the screencast below. It shows how the autoopt tool can be used to illustrate intermolecular interactions - in this case hydrogen bonding between water molecules. Note how the H atoms on one water follow the O atom on the other when you move it (electrostatic attraction), how it's impossible to get the O atoms next to each other (electrostatic repulsion), and how one molecule gets out of the way when you try to push the other too close (steric repulsion).