Boy talk about bad timing. NASA’s World Wind is pretty much the same type of application as ArcGlobe or Google Earth, but unlike either of those two, it is open source. Right away you notice one feature that Google Earth does not have is Web Mapping Server (WMS) support. In addition to that killer function, World Wind also includes LandSat7 imagery, USGS Digital Ortho, USGS Topo and even MODIS. It isn’t a small install at 180 megs, but given the community that has sprung up around it you’ll have even more to download. Plus unlike Google Earth, World Wind’s digital models are as impressive as anything I’d expect from ArcGlobe.