You can keep notebooks stored in plain-text and have them synchronized with a directory on your mobile device, SD card, Dropbox, or over WebDAV.

Create, edit and delete notes and tasks

• Collapse and expand sub-notes
• Schedule tasks and set their deadlines
• Set priorities and tags for notes
• Fling notes left or right to open quick-menus
• Search notes by various properties
• Create and save searches for quick access
• Synchronize notebooks with one or more directories

Notebooks are saved in Org mode's file format. "Org mode is for keeping notes, maintaining TODO lists, planning projects, and authoring documents with a fast and effective plain-text system." See http://orgmode.org for more information.