TiddlyWiki - a non-linear personal web notebook
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.
wikidPad - wikidPad is an application for storing thoughts, ideas, todo lists, contacts, or anything else that user can think of to write down.
Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.
Knowledge Workshop - Learning Management Solutions provides innovative and reliable software for the knowledge worker.
Slack - A messaging app for teams who see through the Earth!