Tiki Wiki CMS Groupware - Tiki Wiki CMS Groupware, also known as Tiki (or TikiWiki), is a full-featured, web-based, multilingual, all-in-one Free/Libre Open Source Software solution. Tiki can be used to create all kinds of web apps, portals, knowledge bases, intranets, etc.
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.
Pmwiki - PmWiki is a wiki-based system for collaborative creation and maintenance of websites.
Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.
WikkaWiki - WikkaWiki is a flexible, standards-compliant and lightweight wiki engine written in PHP.
Slack - A messaging app for teams who see through the Earth!