UpNote - A beautiful and clean cross-platform app for notes organizer

EssentialPIM - EssentialPIM is a free Personal Information Manager that keeps up with the times and lets you manage appointments, tasks, notes, contacts, password entries and email messages across multiple devices and cloud applications.

Notesnook - Notesnook is a simple and private note taking app that keeps your notes organized and synced on your phone, tablet and computer.

Todo.txt - Track your tasks and projects in a plain text file, todo.txt. A todo.

Note Board - Productivity app. Save information like a sticky notes.

Task Coach - Task Coach is a simple open source todo manager to keep track of personal tasks and todo lists.