Planner.el project is an Emacs organizer.
Planner.el is an organizer module for GNU Emacs and XEmacs. It tracks tasks, appointments, and notes in plain text files, which may be published via emacs-wiki.
planner.el is an Emacs module that gives me a summary view of my tasks, schedule, and notes inside Emacs (which incidentally has a nice graphical interface, too). Together with emacs-wiki.el, it lets me easily manage my website.
Another ultra-handy thing is M-x remember from remember.el, which pops up a buffer asking me what I want to remember and stores a note in my daily planner page. For example, this is one such note created by remember.el. A patch contributed by Thomas Gehrlein allows easy navigation of planner pages - simply select dates from M-x calendar.
Personally, I prefer this text-file-based system to Evolution or Korganizer. I remember dropping down to M-x grep to quickly search for something in my daily planner files. I can backup my data files in a .tar.gz. I can perform diffs and version control (although I haven't gotten around to doing so yet!). I can even run it in conjunction with the Remembrance Agent.