Wikis are collaboratively edited websites that allow users to easily add and edit content. They provide features like history and discussion pages. Wikis have advantages like facilitating asynchronous collaboration and leveling participation, but also disadvantages like installation complexity and issues ensuring content quality. Popular wiki engines include MediaWiki, used by Wikipedia, and MoinMoin, PmWiki, and TikiWiki, which are open source options written in languages like PHP and Python.