Microsoft Azure is Microsoft's Infrastructure as a Service platform that allows you to create services with a industry-grade Hybrid cloud.
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Pro Supports running Windows Server
Most, if not all, of the major cloud PaaS providers offer a Linux variant to host your applications. Windows Azure, being a Microsoft product obviously, supports Windows in addition to Linux.
Pro Linux Instances
The Azure platform has been supporting Linux VMs for a while now and has Linux distributions readily available in the catalogue.
Pro Free Tier
Microsoft Azure offers a Free Tier option that allows you to spawn a BST-1 instance that has 750 free hours.
Even though in the context of Pay-as-you-go services, it's cost effective, but monthly pricing for these services are quite higher than competitors.