Optimizely provides start-of-the-art infrastructure for running split-and-multivariate content testing on websites & apps. I have seen Optimizely used cross-organizationally, usually implemented by Engineering and utilized by a Product and/or Marketing. Testing can be targeted to ad campaigns, segmented based on visitor type, or started by more complex, programmatic triggers.
By utilizing Optimizely, organizations can test and iterate how content changes affect Key Performance Indicators (KPIs). It provides best-in-class tools to setup testing & customization, as well as tracking it's effectiveness.
I have several clients that have utilized Optimizely in the past, with one client that still uses it.