I have a help project that has two .NET assemblies. One is the main product assembly, and the other is a common assembly used by multiple products.

 The TOC is OK, except that it wants to use the common assembly Introduction topic as the one to open. I suspect it's because that file name is alphabetically first, because the product assembly is listed first on the Included Modules page.

How can I select which of the two projects the TOC opens with?

I would suggest creating a .html manually that is an introduction to the documentation set, then add that to the additional files and create an entry to point to that file as the first in the TOC.

If you are using HelpStudio, you can do that in there.

I think this answer is ridiculous. I've got a similar situation, but mine is a mature project to which I've just added a second .NET assembly. The second assembly is genuinely secondary, and I'd like my existing introduction to remain the default page for the help, but now I have to re-author it using a different toolset, rework the text and the links to make it apply as an "overall" intro instead of an intro for my primary assembly, because you have not given me control over the default page?

I suppose I could make a vestigial intro that everyone would have to click through to get to the real intro, but that would be stupid as well.

We worked around the problem last time by deciding the second dll, which was used by four products, should be documented as a separate item. But in the next release, we will have a second dll that is definitely subordinate, so we're back in the original situation. (Adding Entity Framework support to the existing product by way of a helper dll)

Plus, my product manager is getting very ambitious about including other material in the help file. Is there any alternative to the "master intro" approach?

I didn't find any alternative; I ended up implementing the "master intro" which is currently rather redundant of the intro to my main assembly. Sigh. Betsy, do please post if you find a workaround.