Free Open Source Screen Recording Software - CamStudio

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CamStudio is able to record all screen and audio activity on your computer and create industry-standard AVI video files and using its built-in SWF Producer can turn those AVIs into lean, mean, bandwidth-friendly Streaming Flash videos (SWFs).

One significant use would be to capture web based trainings which cannot be saved and are available only for a short period of time.
Its definitely not fancy, with lots of features but will work well for easy screen recording.