Optimizely is a website optimization platform that provides A/B testing, personalization, and experimentation capabilities to help businesses make data-driven decisions and improve the user experience on their websites. The "CMS" in "Optimizely CMS" likely refers to its integration with Content Management Systems, such as WordPress, to allow for more seamless optimization of a website's content.

Optimizely was founded in 2010 by Dan Siroker and Pete Koomen. It started as a platform for A/B testing and quickly expanded to offer website personalization and experimentation capabilities. Over the years, Optimizely has grown to become one of the leading website optimization platforms, serving a large number of customers across various industries. In recent years, Optimizely has continued to innovate its platform and expand its capabilities to meet the evolving needs of businesses and digital marketers.