Stickies - Stickies is a PC utility written to replace Post-It-style notes left stuck to your monitor.

Memo - Sticky Notes - Memo is a simple and elegant app for quickly jotting down notes on your Mac.

Pystickynote - Stickynotes for your desktop easily from the command line.

Scrawl - Scrawl is a notes taking and memo app that lets you keep track of the things that are important for you, like daily routine tasks, projects, reminders, calculations, or accountability of someone.

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.

TopXNotes - TopXNotes is a personal notes and information organizing tool that you can use on iOS or Mac OS.