Redmine

+1 In order to use a wiki for some more complex project, it is
necessary to have a possibility of grouping wiki pages into some
logical structure. It may be categories and sub-categories, tags,
or some folder-like structure.

+1 for menu with subtitles in wiki sidebar

I've started to implement this feature. Is there anybody else working on it? I don't want to waste my time :-)

Here's a patch with a first shot at implementing this feature: #3274

Just to be clear here, are we talking about the same thing as adding namespaces to the wiki system? If so I fully support this. We run a school project on Redmine and each year a new group of students shows up and it would be very convenient for us to be able to move all the wiki pages from previous year into that years namespace and start fresh for the new group.

So just to state the requirements we have:
1) Be able to move pages into/between namespaces
2) Be able to have two pages with the same name given that they're in different namespaces, e.g. 2010:MyPage and 2011:MyPage.

At least I couldn't find any other issue related to namespacing wiki pages so I'm throwing my 2 cents in here. If I should create a new issue for this, just let me know and I will.

The most likely implementation of this feature are tags (such as [wiki][feature][tags]). Redmine doesn't include the necessary gem for this yet, but #2897 is an open request to change this. After that it should be relatively easy to add tags to the wiki and issues.

However, I've switched to the ChiliProject fork recently which has faster release cycles. Tagging isn't implemented there yet neither, but it's on the roadmap for later this year. I guess you just have to watch both projects and - if you need this feature that much - continue with whichever gets tagging first.

+1