A system, method, and computer readable medium for usage billing of one or more hosted applications serving one or more clients. The hosted applications are contained within one or more isolated environments or run without isolated environments. The system may include usage billing based on one or more of resources open, amount of data flowing through resources, number of open files, number of transactions, number of concurrent users, number of processes, CPU utilization and memory usage, The system may further include a management interface where administrators may add, remove and configure isolated environments, configure client policies and credentials, and force upgrades. If using isolated environments, the isolated environments may be isolated from other applications and the host operating system on the clients and applications within the isolated environments may run without performing an application-installation on the client.