Step diagrams are what lawyers call flow charts, but with a design convention language that's a bit like UML, and with tons of meta data attached to each element. There's also a time dimension as you can step through to see each stage of a legal process.

I understand what they are as a dev but I'm not a lawyer so I can't point you to anything more unfortunately.

Was this company called Checkbox?

It's a subset of process mapping specific to the legal area. Since there is no agreed upon convention for process maps everyone does their own thing and calls them slightly different things. I tend to just use the six sigma convention even for non six sigma things.