PageMill is a web editing/design software package for both Macintosh and Windows produced by Adobe. It was discontinued after version 3.0 in favor of their far more powerful GoLive software.
PageMill is still the best WYSIWYG web editor for those who are using older Macintoshes that lack sufficient RAM and hard disk space to run GoLive or Dreamweaver. Being obsolete, it can be obtained cheaply and doesn't hog your system resources.
PageMill was a competitor with FrontPage in Windows, and in my experience PageMill was a bit more elegant and useful. People with older PCs may likewise find PageMill to be the superior software if they can't upgrade to more sophisticated packages.
It's also useful for folks who are proficient with desktop publishing programs like PageMaker or Quark but who don't have the time or inclination to learn modern web design software. If you know common DTP software, you can quickly get up to speed with PageMill and put up a decent-looking home page. There are new things to learn, of course, but the program comes with a useful tutorial.
If you're the low-tech web editing sort who prefers to use BBEdit to hand-code your web pages, PageMill is useful to keep around to quickly create tables and frames.
PageMill has the annoying tendency to insert all sorts of extraneous tags (extra spaces in tables, unnecessary tags in image commands, etc.) that muddy up your code and can mess up your layout. So, if you've got an HTML file you simply need to edit, or you need to make a new page that could simply involve changing the text of a page you've already created, it's best to use BBEdit or TextPad and leave PageMill for when you need to create something completely new.
One would think that Adobe products would play together well. In the case of PageMill on a Mac, one would be wrong. If you run PageMill and then try to run PageMaker (either concurrently or after you've quit PageMill), PageMaker will very likely crash soon after launch. However, if you start up PageMaker before you run PageMill, things will be fine. If you've been using PageMill and then decide to run PageMaker, restart the computer first.