You see some gasoline particles which are flying around. Some are colliding with a wall, some are aggregating. One Wall is movable but attached to a spring. Everything is calculated by the law of physics and can be manipulated with the mouse.
The second video show other new features: instruments. Currently there are four: note, meter, controller and graph. Using them you can create an interactive demonstration around you experiment like the one shown in the following screencast:
There are a couple of other nice new features. I think I will create other videos soon. If you cannot read the text in the videos view them in fullscreenmode. YouTube reduced the video quality so much...
You can see all of this and more yourself by compiling Step from SVN and trying experiments from "examples" folder.
Thank you for your attention. Please post comments to these videos or this blog.
Step -- http://edu.kde.org/step/