The whole Open Stack thing is getting interesting. The compute part is called Nova.
Nova is a cloud computing fabric controller (the main part of an IaaS system) built to match the popular AWS EC2 and S3 APIs. It is written in Python, using the Tornado and Twisted frameworks, and relies on the standard AMQP messaging protocol, and the Redis distributed KVS.
It seems to be highly influenced by Amazon cloud. The part I like a lot is that it is Python-centric. The other part of Open Stack, the object storage part known as swift, is also written in Python.
Swift is a highly available, distributed, eventually consistent object/blob store.
A note on AMQP – Advanced Message Queuing Protocol.
The Advanced Message Queuing Protocol (AMQP) is an open standard application layer protocol for Message Oriented Middleware. The defining features of AMQP are message orientation, queuing, routing (including point-to-point and publish-and-subscribe), reliability and security.
Nova uses RabbitMQ, an implementation of AMQP (written in Erlang!), to support a shared-nothing, messaging-based architecture.
Nova is built on a shared-nothing, messaging-based architecture. All of the major nova components can be run on multiple servers. This means that most component to component communication must go via message queue.