if you have a project, how do you write the documentation?
I know there was substantive thread not that long ago, here in Chit Chat I think. But, can't find it now (seems like Chit Chat is not searchable - or i just didn't ask the right questions).
That thread dealt with
commenting one's code and heading one's function sections etc. etc. That's about the best way to do this documentation.
But, if you want to go further then I once installed Docuwiki on a server which was private : so it would be a bit similar to the examples in the posts above. A friend of mine just wrote a set of PHP scripts that wrote to a text file - just because this meant an ordered way of entering the details for the documentation and then presenting it later on - and, of course, it was searchable. Not a very complicated thing to knock up and doesn't have to be "databased".
The above assumes that this documentation is simply for your own reference and not as user notes / manuals for users who have purchased a software product from you. Then one of those above would do I guess.
But, nothing beats a set of good comments within the code's text - this is good for others who may end up maintaining your code later and largely irrelevant to purchasers of the product.