VLMC (VideoLAN Movie Creator) is an open-source movie creation tool. It can be used to create clips and edit videos. The project hasn't been updated for a while, and I found it very hard to find the downloadable DMG for the Mac on the project's website. Versions for Windows and Linux are easier to come by.
When you first launch the application, you will see a disclaimer that warns you about the pre-alpha nature of the application. After you accept that, you will see the project creation wizard, where you set the size and type of your video and give your project a name and description.
In the main window, you will see a list of effects that you can add to your videos, a player that lets you quickly and easily play any videos that you have added to your project and a timeline where you can add and time effects. The list of effects is on the pane on the left part of the screen. You need to drag and drop them to add them to your project.
From VLMC, you can upload video to YouTube directly. This is a very nice feature. In my testing, I was able to create a project and add a few effects. Then I was able to export the project. I had the application crash on me a couple of times, but that is to be expected from a pre-alpha app.