USinternetworking, Inc (Annapolis, MD) is a large ASP concentrating in ApacheLinuxOpensshPeopleSoftPerlPython application hosting and management. We administer a network of over two thousand machines and 15 different operating systems with a custom in-house developed monitoring and administration application that is based primarily on Open Source software including , , , , and . Proprietary monitoring solutions were evaluated but in all cases were both too expensive and too difficult to integrate effectively with our particular set of network and application configurations. Open Source software has enabled USi to significantly reduce costs while at the same time deliver a higher level of application availibility and reliability to our clients.