Apache JSPWiki - Apache JSPWiki is an open source Wiki engine, feature-rich and built around standard JEE components.
Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
DokuWiki - DokuWiki is a simple to use and highly versatile Open Source wiki software that doesn't require a database.
Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.
MediaWiki - MediaWiki is a free software wiki package written in PHP, originally for use on Wikipedia.
Slack - A messaging app for teams who see through the Earth!