Each department winds up writing its own wiki page about the same topic (say, Topic X), and they're all different.
So it means most of your departments work on something very similar?
Not exactly. Each team treats its wiki as "The" wiki, and they create general-purpose articles like "How to request a day off from your manager" and "Where is the company cafeteria" that apply to the whole company. Individual writers do not think about the big picture, that general-purpose articles might belong a different, general-purpose wiki. They just want to get their job done quickly. So these kinds of articles get written in the wrong wiki, or in several wikis at once, and they drift out of sync. With a single, central wiki, this is much less likely.
Imagine if Wikipedia had a separate wiki for every city in the world. The same problem would result.
Do you have any extensions or modifications that you would like to make public & free & open source? Or maybe you even already did it with something? :-)
Indeed, we are working out a way to open-source some of our extensions.
DanB