Today, Linux is an enterprise-level operating system. It is robust and exploits numerous standards and new technologies.
Linux is an example of an Open Source project. Distributions include Open Source tools in their packages. The actual expense for using this operating system in your business can be significantly less than for other operating systems.
Open Source signifies freedom for developers to work on projects in which they take an interest. This is an attractive premise, and many talented developers work on Open Source projects. The scrutiny of many Open Source community members makes code quality high.
Distributions solve a perceived problem with Open Source: who is responsible for ongoing software support? Distributors (and others such as IBM Global Services) take care of support and maintenance in a legally binding way.