I've tried using VisIt (and Paraview) a few times but have never really dedicated myself to it. It looks so nice and seems so powerful. I just haven't been able to get it working in a way that allows me to quickly and quantitatively (with data labels) explore multiple axial levels of a nuclear reactor state and step through time to see how the shuffling algorithms did and whatnot so I keep sticking to this specialized .NET thing an intern wrote 7 years ago. I'm sure VisIt can do it, I think I just need an expert to teach me or something.