Nimbus 2.10.1 - Bird's Eye View
In a nutshell, Nimbus allows a client to lease remote resources by deploying virtual machines (VMs) on those resources and configuring them to represent an environment desired by the user. This is known casually as cloud computing (one definition of it), a little more specifically as an "infrastructure-as-a-service" (IaaS) solution.
Also included in a Nimbus installation is a storage cloud implementation called Cumulus that has been tightly integrated with the other central services (but it can also be used standalone). Cumulus is compatible with the Amazon Web Services S3 REST API, but extends it as well (to include quota management, for example).
A set of software needs to be installed to one service node in a non-root account and a separate piece of software needs to be installed on any number of virtual machine monitor (VMM) nodes (some root permissions are required).
There is also a separate download for a client called the cloud client that makes life very easy for users.
Clients interact with the service using credentials over multiple protocols. The easiest client to use is the cloud client (details) which is geared towards getting users up and running in minutes. The service must be configured in the cloud configuration to serve requests from the cloud client. These clients implement web services messaging (specifically WSRF based).
But Nimbus also provides an implementation of Amazon's Elastic Compute Cloud (EC2) that allows you to use clients developed for the real EC2 system against Nimbus based clouds. See the EC2 Clients page.
You can examine the web services based interface details in the WS interfaces section.
Nimbus also allows clients to create auto-configuring clusters. Starting one VM is somewhat straightforward, but launching 10s or 100s together can become laborious without heavily customized scripts. Nimbus provides a general solution to this problem, one that allows you to even store VMs with no private credentials on-board. For more information, see here.