Applications

A wiki is usable for quite a few applications, because there few requirements to use it and the content can be anything. You can use it for everything that can be displayed by linked text pages.

Examples

personal notes (instead of wasting paper)
conference protocols
to-do lists
news on wiki homepage, asynchronous communication
common creation of documentation
brainstorming
personal or collective link lists
efficient alternative to e-mail or phone
much more