Wikis can focus on a particular subject area, enabling researchers in the field to develop a specialist resource such as a community of practice, online manual etc.
They are particularly well-suited for content which needs to be regularly updated.
As wikis are generally easy to use, they are a great way of enabling members of the public to contribute to a research project, such as 'crowdsourcing'. They can be configured to allow as much editorial control as required.
Some examples are below:
Here are some other types of collaborative editing tools.
The Digital Humanities awards highlight interesting projects around the world. They include a category for projects which have failed, so there is plenty from which to learn....