In working with my company's offshore developers, I was tasked with providing them documentation on a set of class libraries we use in our applications. In the .NET 1.0/1.1 time frame, we used NDoc, which, sadly, passed away last year, to turn the XML comments output by the C# compiler into CHM help files. After a bit of googling and a false start, I discovered Sandcastle, which Microsoft uses to build the .NET Framework documentation itself. I also discovered from the Sandcastle blog that it takes a whole mess of manual steps to use, which appeared daunting at first glance, and, being a programmer, I was looking for an easier (lazier) way.
From the official Sandcastle download page, I found the Sandcastle Wiki, and from there, an NDoc-like, Visual Studio-like GUI for it creatively titled Sandcastle Help File Builder. Setting up a SHFB project and getting the documentation to compile, and then to look/behave almost exactly like I envisioned, was simple at this point.
Overall, I'm pretty impressed how easy it was to discover this and find resources to use it--a lot easier than it used to be to fill a component/tool need that Microsoft claims to address (some of the data access pieces in the Visual InterDev 6.0 time frame come to mind). Really, the hardest part was getting the Google terms right!
Again, you can download Sandcastle here. The latest version is the June 2007 CTP (Community Technology Preview, which you probably already know means it's pre-release), released a couple weeks ago.