Vabotu - More than slack. More than Trello. FREE.
MediaWiki - MediaWiki is a free software wiki package written in PHP, originally for use on Wikipedia.
Do - Do helps you run productive meetings. Do work you love.
TiddlyWiki - a non-linear personal web notebook
Kurator - The premier Chrome extension for savvy researchers and publishers alike. Curate your interest and publish to your website, newsletter and social media sites directly from the browser.
Confluence - Confluence is content collaboration software that changes how modern teams work