Practical TLA+: Planning Driven Development

I found this book to be an excellent guide to the world of "using a tool to help you think good about software design." A few points:
- it's not just for doing fancy distributed systems, you can also use it to help reason about complex product requirements
- since it's a tool for reasoning about systems in general, you don't even need to limit yourself to software!
- the first half is a little bit dry so I quit after that. Don't do this, I went back to it and the second half is so worth it - lots of insights and practical advice and wonderfully written examples.

Also it's quite short. So: if you want another way to think about the behavior of systems pick this book up and read the whole dang thing.