Although Amazon, Google and Microsoft are the big players, everyone and their dog are implementing clouds. There's even an open source cloud: https://www.opens

Although Amazon, Google and Microsoft are the big players, everyone and their dog are implementing clouds. There's even an open source cloud: https://www.openstack.org/ https://www.openstack.org/ This is being used by some large companies (e.g. HP), and can also be used by companies who want to run a VM setup on their own hardware like they probably already do with VMware, but want a cloud-like API for it.