I'm the author of Hummingbird. I originally built it for the flash sample sale site Gilt Groupe, to visualize the gigantic traffic spike that happens at noon. (from 20 req/s to about 2000 req/s then, probably at least double that now)

Since then I've been slowly building out some features that are more useful for smaller sites, like the map view. The awesome mapping library is PolyMaps, using CloudMade tiles.