Free tool to create a screencast to upload on hosting video platforms
This can be accomplished with QuickTime Player in Snow Leopard. From the File menu, select New Screen Recording. When you have finished recording, the video file will be opened for playback and from the Share menu, you can select YouTube....
For some reason, it was difficult to find this question, but I'm glad sentinel pointed out the solution I ended up using as well, which is QuickTime Player.
What I'd like to add is how to capture system audio as well. This is in Mountain Lion (10.8).
There's a free, open-source tool called SoundFlower which creates a virtual input/output audio device. After installation, go into ‘System Preferences’ -> ‘Sound’, and from the ‘Output’ tab select the ‘SoundFlower (2ch)’ device. (If your application allows it, you may also change the output device just in the application you're recording.)
Now, in QuickTime Player, open a new screen recording, and click the little down arrow on the right side of the window. From this drop-down menu, also select the ‘SoundFlower (2ch)’ device. Now record as normal.
The only problem with this solution is that you won't hear the application's sounds anymore, even though they're now being recorded. But there's a solution for that too: a multi-output that outputs to both your normal output and the virtual SoundFlower device.
Launch ‘Audio MIDI Setup’, either using Spotlight, or look in /Applications/Utilities/. Click the plus-button at the bottom left of the list of audio devices, and select ‘Create Multi-Output Device’. Now, with the new device selected, check the ‘Use’ boxes for your normal output device and the SoundFlower device.
On the left, expand the ‘Multi-Output Device’ and make sure there's a small clock icon next to your normal output. If not, right click it and select ‘Use this subdevice as the master clock’.
Now you can set this device as your output, either straight from Audio MIDI Setup by right clicking it and selecting ‘Use this device for sound output’, or by selecting it in ‘System Preferences’ -> ‘Sound’ from the ‘Output’ tab. You'll both hear and record system sound now.