Agile is a methodology that focuses solely on the development of software. Agile aims to iterate development, establish continuous delivery, shorten feedback loops, and improve team collaboration throughout the software development life cycle (SDLC).
Lean IT is a methodology that aims to streamline the value stream of the product development cycle. Lean focuses on eliminating unnecessary processes which do not add value and creating a flow to optimize the value streams.
DevOps focuses on both the development and deployment — the Dev and Ops of the product development process. Its goal is to effectively unite the roles between automation tools and IT professionals for a more streamlined and automated process.