Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
DokuWiki - DokuWiki is a simple to use and highly versatile Open Source wiki software that doesn't require a database.
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.
Wiki.js - An open source, modern and powerful wiki app built on Node.js, Git, and Markdown.
Remember The Milk - Remember The Milk is a task and time management application for mobile devices.
TiddlyWiki - a non-linear personal web notebook