Lifeograph offers a rich feature-set for note taking, to-do management, and a more:
Supports encrypted (with real AES256 encryption) and unencrypted diaries
Automatically logs out when not used for some time (to protect your diary when you forget to log out doing some other thing) (optional)
Automatically formats entry titles and subheadings
Wiki-like rich text formatting (*bold*, _italic_, =<strike>strikeout</strike>=, etc…)
Text searching & replacing with a list of matches
Advanced filtering with combining different filterers with AND or OR
Themes in text editor with support for background images and a few stock themes
Favorite entries
Integrated map for travel notes and planning
Various to-do management features, including completion percentages
Very strong support for tagging, including parametric tags and inline tags for paragraph level tagging
Spell checking
Links between entries, and to URIs (http://, file://, mailto://, etc…)
Multiple automatic backups to prevent data loss
Printing individual entries or whole diaries
Statistical charts and some serious analytical capabilities (when combined with parametric tags)
Extraction of data from diary into tables which in turn can be pasted into spread-sheet programs
Images and charts in entries
Synchronization of diary files with each other (such as different versions on different machines)
Export diary file to plain text