HTML5 Canvas makes it possible for users to draw images directly in the web browser. We want to use this functionality to let users quickly draw simple image diagrams / illustrations to better explain their technical questions or answers. Here is the minimal feature set that we are looking for, starting with estimated importance, or estimated frequency of use:

• (70%) - most often used - free-form brush drawing with various brush thickness and colors
• (10%) - simplest possible UX for typing text
• (10%) - simplest possible UX for drawing rectangles, lines and circles
• (3%) - eraser brush

Let's make ANSWERS to include SCREENSHOT and review of exactly ONE editor per ANSWER, so we could vote up on the answers and collectively decide what is the best javascript canvas image editor script. Thanks!