Most of the issues with Confluence I've seen are lack of organisation, out of date information mixed with up to date pages and really poor search / discoverability. The fact that people can just edit or create a page at any point is one of the better parts because it's easy for someone to fix something up during onboarding, during a drive-by consultation etc.

There are Wiki-like interfaces for git+Markdown: GitHub's wikis, gitit, and more.

Google Docs