Who are dominating the Enterprise IT industry?

A great deal of enterprise software is now available through the free software movement, notably operating systems, web servers and databases.

Many other types of enterprise software are also being introduced, such as application servers, portal servers, and even productivity software that is well suited for large-scale adoption by enterprises. While most open source software is available freely for use and further development, several companies provide enterprises with open source enterprise software for free and charge for software maintenance, modifications, support and additional functionality.

Useful resources: http://www.hoovers.com/free/search/simple/xmillion/index.xhtml?query_string=sap&which=company&page=1&search_x=0&search_y=0