This is a simple gpu-accelerated mandelbrot set viewer using WebGL. It employs the smooth iteration count as described in Inigo Quilez's article. If your framerate is bad (as indicated in the upper left corner of the viewer) you might want to lower the settings. You can also export a render using the save button. Sadly you can not zoom in indefinitely: I know of no way to do arbitrary-precision arithmetic on a graphics card.
You can pan by dragging with your mouse, and zoom by scrolling with your mouse wheel. If you're on a touch device you can pan & zoom in the standard way.