Online screen recorders require Java 1.5 and a supported web-browser:

• Screencast-O-Matic

Freeware based video screen recorder. It allows you to create a screencast of a specific region of your desktop or a full-screen screencast. Screencast-o-Matic can record video with audio. You can also add notes to your screencast at specific times. Also allows to add visual hints to your screencast: the cursor size can be increased and mouse clicks can be highlighted with a circle (to make it easier for people to follow the mouse).Screencast-o-Matic is using a Java applet (requires Java) to do the screen capture and playback so theoretically it should support all major platforms and browsers. The max length of a screencast is limited by 10minutes if you upload the video to YouTube.

Screen capture software for Linux

1. Istanbul (Linux) is a desktop session recorder for the Free Desktop. Istanbul allows to create screenshots and screencasts. It records your session into an Ogg Theora video file. To start the recording, you click on its icon in the notification area. To stop you click its icon again. It works on GNOME, KDE, XFCE and others.

2. recordMyDesktop (Linux / open-source) produces a file(default out.ogv) that contains a video and audio recording of a linux desktop session. The default behavior of recording is to mark areas that have changed(through libxdamage) and update the frame. This behavior can be changed (option --full-shots ) to produce a more accurate result or capture windows that do not generate events on change (windows with accelerated 3d context), but this will notably increase the workload.
   recordMyDesktop doesn't have a commandline interface.

3. xvidcap(Linux/BSD/UNIX-like OSes / open-source) - a small tool to capture things going on on an X-Windows display to either individual frames or an MPEG video.

4. vnc2swf(Linux, FreeBSD, Solaris, Mac OS X, and Windows) is a cross-platform screen recording tool for ShockWave Flash (swf) or Flash Video (flv) format

5. Krut Computer Recorder freeware open source screencasting software. It allows record video from webcam, capture device or screen. Krut allows to record videos with sound, of selected parts of your screen. The recordings use the quicktime .MOV format. In addition to a movie file, the program also records separate files for audio (wav) and video (mov), which easily allows encoding to any movie format using an external encoding program.Krut uses quick buttons to start recording, take a screenshot, and change the recording area. Krut is written in Java and well suited for making video tutorials (instructional videos) on most platforms

6. cpsrecode, capseo and KWin
   KWin in KDE 4 offers the possibility to record desktop. The resulting files have a .cps suffix (cps = capseo = video codec created by the same developer as the underlying library called captury.

7. SimpleScreenRecorder  which is an opensource video capture / screencast very fast and offers good codec choices (notably x264).
   
   As a side note none of the listed softwares really statisfied me (either way too slow or poor video quality because of poor codecs).