The VLC mediaplayer is opencource and crossplatform.
It has a screen capture device, that lets you record the screen.
Note: There is a drawback…if you want audio in your video you’ll have to record this seperately.
Download it from here: http://vlc-media-player.en.softonic.com/
NB! This procedure was made running VLC v.1.1.12 on Mac OS 10.5.8
Quite different procedure for windows with unknown version of VLC found here: http://pctonic.net/use-vlc-as-a-screen-recording-tool
Start screen casting by opening the VLC player, select File>Open Capture Device
choose screen in the dropdown menu. If it’s already chosen and you don’t see any settings panel, choose something else from the dropdown menu, then choose screen again.
It should look like this:

These settings shown here, will give you a small square around the mouse, whereever it is while recording. The frame rate settings gives you a smooth recording.
Press settings…

Start by choosing an encapsulation method. I recommend AVI.
Press ‘Browse’ to set where the video file should be stored on your computer.
Add the rest of the settings. Press OK.
You’ll then see the screen from before. Press Open, and your recording will begin.
When you are done, activate VLC media player and select Playback>Stop.
Your video has now been added to the location you pointed to in the settings.
A list of alternative screencapture software here: http://en.wikipedia.org/wiki/Comparison_of_screencasting_software