We are a small company, with projects requiring 1 to ~5 coworkers at a time, that are nearly never in our own offices. In short, we are highly distributed and have very rare chances to spread knowledge internally.
Now we want to change that and achieve some progress in knowledge management, firstly by using our centralised wiki, using internal articles, reports and themed topics related to the fundamentals of our work, that should be written and reviewed by our coworkers.
The wiki has been there for a long time already. It does not look very nice and usabilty could be far better, but it is usable. As it was an expensive piece of software there is currently no chance to replace it with another.
The point of this question is, how can we motivate our coworkers to contribute to the wiki? What kind of incentives (other than money) can be practical?