I started off writing the OpenHeatMap renderer for Flash using Flex3, and then ported the code to vanilla Javascript to support HTML5. There were many things that felt poorly designed in Flex, but the 2D geometry support was a pleasure to use. To minimize the differences between code for the two renderers I ended up rewriting the bulk of the Matrix, Point and Rectangle classes in Javascript. Today I needed to reuse some of my OpenHeatMap functions in another project, so it seemed like a good chance to split off the classes and relicense them as BSD.
Why should you care? You almost certain don't, unless you're somebody who's porting a big project from Flash to Javascript. In that case you're probably sobbing in a corner, rocking back-and-forth and clutching your knees, thanks to all the other painful issues you're dealing with. If you emerge from your fugue state long enough to notice, you'll be happy though, trust me.
The code's up at https://github.com/petewarden/flxjs.