In the beginning, hell yeah, a calculator and notebook/logbook. Still used the calculator and notebook for the first five years of my pro career.
Got a copy of ProMash when I switched gigs once, and still use it, primarily for liquor calculations and record-keeping. I tend to lose notebooks due to not brewing every day anymore...
Even after I got ProMash, I used a pad of graph paper to track ferments, just like I started doing in my first gig. Bell curves rool. And I kept a logbook. I always kept paper records for convenience's sake when I was a pro, should ATF or the excise ever want to peruse my records.
But to answer the OP most clearly, most 'big boys' don't really need software. You kind of know what you're going to get from what ingredient in what batch size. It's like professional chefs, really; you get to know your ingredients and how they play together.
For example, I never really used software to determine things like gravity and IBU. When my minimum batch size is 10bbl, I'm not measuring 2 pounds of this malt, 3 pounds of that malt; I'm using whole and half sacks. Keeps things simple when ordering ingredients and at dough-in. Say I know I get a gravity of 1.055 from 9 sacks of pale and 1 sack of 55L crystal. If I want to brew a different beer with that gravity, I can use 4 sacks of pale, 3 sacks of Munich and 3 sacks of Vienna and get something completely different.
Same goes with hops. If I know I get a certain amount of bitterness with a pound of Target at 10% AA in 10bbl at OG 1.055, I can use that datum as a way to arrive at a new bittering charge in a different beer, without resorting to software.
Anyway, that's gross oversimplification with holes big enough to drive a truck through. But what I'm trying to convey is so internal, so "you have to be there" that it's hard to explain. You just know, you know?
Bob
Cheers,