This book is a classic. It's positioned as a "marketing" book but it's one of my go-to books for thinking about SaaS product development when you're seeking out product/market fit.
The Customer Adoption Life Cycle is one of those quintessential diagrams you pin to your work wall - it's all from this book.
Strongly suggest reading for anyone thinking about how to evolve your product, especially for SaaS offerings.
Also it's very interesting exercise to have someone lay down the strategy & only then read the book. Completely changes the perception of features and market from product/market fit point of view.
Buffer
WakesApp