A very fast JavaScript library for geospatial point clustering for browsers and Node. A work in progress.
var index = supercluster({
radius: 40,
maxZoom: 16
});
index.load(points);
index.getClusters([-180, -85, 180, 85], 2);
Modified to add convex hulls to the clusters, allowing display of that as the marker, rather than a point.
Demo still needs work as far as coloring by density, and some better labeling.