Visual Studio does have its own ability to create a help file. Here's the home page of Paul O'Rear's blog. http://blogs.msdn.com/b/thehelpguy/ You will also find information at http://www.helpware.net. You need to research that to find out if that would suit. This is not the forum for that topic.
Aside from that, the first issue is where is the help going to reside? If it is on a web server, then WebHelp would be an option. That can also be run locally but you may encounter some issues if you need links to PDF files. If the help is going to be installed locally, what's the objection to CHMs? In RoboHelp 10 they can be skinned to look like WebHelp.
See www.grainge.org for RoboHelp and Authoring tips
We have just done the following with RoboHelp 9.
We generated one CHM. We then used the MshcMigrate utility to migrate it into the new Microsoft Help format.
It is viewed in the Microsoft Help Viewer 1.1.
We tried working with merged CHMs, but the migration could not be easily automated.
I imported all files (from all of the children CHMs) into the parent CHM and I put a placehoder for each of the child TOCs (using the "Insert TOC Placeholder" icon in the TOC pane).
You cannot have more than one TOC entry pointing to the same RoboHelp topic. If you do, you will get an error topic when clicking on that TOC entry.
You also need a main parent book in the TOC and put everything under that. You need to have a topic attached to this parent TOC entry.
So, in the image below, "MGHELPW" is the main parent book and all the other books are under it.
MGHELPW is taken from the name of the CHM. Rename the CHM if you want a more relevant name here.