Citrix XenApp and its close cousin Citrix XenDesktop are generally useful platforms for application and desktop virtualization, respectively. When done correctly, virtualization of these asset classes can yield substantial advantages for an organization, such as cost reductions in IT operations, superior flexibility in supporting remote sites and employees, and broader access to apps and desktops in Linux-based environments.
VMware is best known for its pioneering efforts in server virtualization, which it brought to the fore of enterprise IT throughout the 2000s. Building on that technical base, the company has since become a central player in every important sector of modern business technology, from network virtualization (through NSX, a billion-dollar business it created from its acquisition of Nicira Networks) to private cloud (via the vCloud Air product lines). VMware has also made inroads in mobile device management (also known as enterprise mobility management), primarily through AirWatch.
The Microsoft Azure cloud has evolved significantly since it first launched as Windows Azure in 2010. It now hosts public and private cloud services, with support for compute, storage and networking workloads across the globe. Recent additions such as Azure Stack (i.e., a solution for running Microsoft hypervisors in your own data center) and Azure Transition Service (which simplifies the migration of IT infrastructures to Azure) have broadened the platform's reach and helped build its market share in the highly competitive infrastructure-as-a-service and platform-as-a-service spaces.
Software-defined solutions - for networking, storage and entire data centers - have become much more prominent over the last decade, as the essential technology underpinning them (virtualization) has gone from the fringes to the forefront of IT. Enterprise vendors such as VMware as well as cloud giants like Google, Amazon and Microsoft pioneered the concept of separating various IT components from the actual hardware that supports them.
