We have about ten engineers, so nowhere near the size where people consider formal methods "appropriate". Nonetheless it's still been incredibly useful for our work.

I'm a pretty huge evangelist of TLA+, but I don't think it's the silver bullet of software correctness. It just happens to be the tool I'm most familiar with and the one I thought could benefit most from a free guide. If people start widely using TLA+, I'll be ecstatic. If people ignore TLA+ but start widely using Alloy, I'll still be ecstatic. Software correctness is a really huge field and there's lots of really cool stuff in it!

Speaking of making methods more accessible, I'm working on a tutorial about Stateful Testing. Hypothesis (https://hypothesis.works) is an absolutely incredible property-based testing library for Python, and I think it could potentially make PBT a mainstream technique. One of the more niche features is that you can define a test state machine that runs by randomly selecting transitions rules and mutating your program state, then running assertions on the new state. It's really neat!