Mandelbrot symbolics in the browser
You can try it out at /mandelbrot/web/, there's no documentation to speak of but hopefully the examples should be enough to get you started. Some calculations can take a long time, but GHCJS's scheduler avoids the dreaded browser "script taking too long" popup, provided the calculations are not in a synchronous callback (thanks to luite in the #ghcjs IRC channel on freenode for pointing this out).
The source code for the web interface is at mandelbrot-web which also requires my mandelbrot-symbolics and mandelbrot-text libraries. You can also download the compiled web interface as a tarball: web.tgz. It has been postprocessed with closurecompiler, as documented on the GHCJS deployment page, which reduced the size quite a bit. Pro-tip #2, Debian calls the nodejs binary "/usr/bin/nodejs", but npm packages expect just "node" - I put a little script in ~/opt/bin/node (which is in my $PATH) to make it work properly:
#!/bin/sh exec nodejs "$@"