Ranked in these QuestionsQuestion Ranking
Pro Libre/open source
Pro Cross platform
Emacs runs on all platforms, Windows, Linux, OSX, even Android and IOS
Pro Can be as simple or as complex as you want
Org mode started out as a simple outlining/note taking app. Then each outline heading can optionally be a TODO list item. And if you desire, you can add SCHEDULE and DEADLINE dates. (Schedule being the date you'd like to start the item.) You can customize the TODO states to add things like DELEGATED, WAITING, BLOCKED, etc.
Pro Exports data to PDF, LaTeX, HMTL and other
You can even build presentation or blog from your data
Pro Supports tables with formules (quite powerful!)
Pro Plain text data storage
Pro Inline image displaying
Pro Free but copyrighted
Pro Fast interaction
Once muscle-memory sets in, can be much faster to use than a point & click program.
Pro Uses Emacs
Pro All apps
Con Obtuse documentation
The documentation assumes a level of understanding of basic Emacs usage that not all users may have.
Con Complicated to get started
Con Difficult to use as a database
For example, if you need to quickly populate client details on quotes, unfortunately its easier to find, copy & paste.
Con Not suitable for normal users
Not even a majority of software developers can be bothered to use Emacs (or VI, for that matter).
Con Uses Emacs (for those who prefer vi, menus, etc.)
Con PDF export can be difficult
Latex assumes you're a (compliant) student, have to do a lot of research to get what you want out of it.