I'd like to briefly point out an issue that I have experienced a few times. I think it's important for scientific practitioners to clean up and package code to the point where other people who are interested in the work have a fighting chance of actually running the code themselves. I do my best to meet that expectation. On the other hand, however, I am not a software engineer, and so my code is not always perfect in terms of steering users away from footguns or testing all edge cases. So if you try any of this code, which I sincerely hope you do, and experience something working way differently (often much worse) than a paper or figure or example file suggests, please reach out to me before writing off the code or method completely. There is a non-negligible chance that I just haven't enforced some aspect of proper usage that may be obvious to a practitioner in that field---such as sensibly enumerating the observations when assembling a hierarchical matrix approximation---but that may not occur to somebody who is just trying out the code or who isn't particularly familiar with the field. While I obviously do my best to try and enforce proper usage through the code design itself, it is challenging and I make mistakes. So please do reach out if you experience surprising things when trying any of these software packages. There might be an easy remedy, and you might save future users similar frustrations.

As a second small rant, if you use any of these packages in your own research in a way that substantively helped your project, *please* do cite them appropriately. Almost all of these packages are companions to a paper, or the README of the package will have citation instructions. As an example, please cite the "Fitting Matern..." paper if you use BesselK.jl to fit a full three-parameter Matern model. It may seem like sort of a trivial software dependency, but in this hypothetical you're really using that package to do something that for decades hasn't really been reliably possible. So please do acknowledge the work that did make your results possible.

I write all software using the GPLv2 license unless otherwise specified.