Markdown by DaringFireball - Text-to-HTML conversion tool/syntax for web writers, by John Gruber
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.
GitHub Flavored Markdown - GitHub uses "GitHub Flavored Markdown," or GFM, across the site--in issues, comments, and...
Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.
Texy! - Texy! is a lightweight markup language as well as converter of this format to XHTML, in a form of a...
Slack - A messaging app for teams who see through the Earth!