Windows Server is the most popular choice for the most important packaged applications at North American enterprises — but the market is not settled by any means. Firms name a wide variety of operating systems (OSes) that they use for critical apps, and 29% name two or more. More than half of North American enterprises would consider switching OSes, and among them, Linux is the top choice, with 37% of switchers. For technology marketers, this means that the OS diversity that they face will increase, not decrease — and that they should start to look at software-based virtual appliances as an alternative to supporting the growing variety of OSes for enterprise applications.