The large amount of data produced by the ATLAS experiment needs new computing paradigms for data processing and analysis, involving many Computing Centres spread around the world. The computing workload is managed by regional federations, called Clouds. The Italian Cloud consists of a main (Tier-1) centre, located in Bologna, four secondary (Tier-2) centres, and a few smaller (Tier-3) sites. In this contribution we describe the Italian Cloud site facilities and the activities of Data Processing, Analysis, Simulation and Software Development performed within the Cloud, and we discuss the tests of the new Computing Technologies contributing to the ATLAS Computing Model evolution, namely Network Monitoring, Software Installation and use of CVMFS, Virtualization and Multi-Core processing.