HowHive - Knowledgebases for teams and companies of all sizes. Knowledge sharing and finding made simple.
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.
Raneto - Open source, flat-file Knowledgebase platform that uses static Markdown files
Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.
openKB - openKB is a Markdown Knowledge base application (FAQ) built with Nodejs and ExpressJS.
Slack - A messaging app for teams who see through the Earth!