Screenr will record up to 5 minutes of video at any resolution up to 2560×1600 on a PC and 1920×1200 on a Mac. You can use a microphone to record narration but there is currently no facility to annotate over the recorded image[s].
No software to install just go to the website, record and save.
Requirements: Browser and Java.
Edit: Not in the 'Downloads Forum' because, well, it is not a download.