Kaizen (which is Japanese for "continuous improvement") is a concept inside of Lean, nothing something opposed or a substitute for Lean. Checkout a book called "The Toyota Way". Is about manufacturing not software, but it will help you sort out the concepts about Lean Manufacturing.
The thing you should focus when thinking about Lean is elminating waste: muda, muri and mura.
People often refers to tools used in lean manufacturing as being lean. The most common tools is probably kanban.
Regarding DevOps, I never saw it's point. It's, at least for me, just a fuzzy concept and a vacuous rebranding of existing ideas. Maybe I just don't get it.
There's a ton of books on the Toyota Production Systems and lean. Most relate to manufacturing but it's not really difficult to translate some concepts to software development. There's a few authors who talk a lot about Lean Software Development but I never really liked most of what I saw and I prefer the manufacturing books myself.