Man, where do I start? org-mode is Emacs’ Killer Application. It started out as an very capable outlining tool, but has grown and mutated and now people use it for time management, blogging, presentations, spreadsheets, GTD, you name it. Org-mode is the reason I returned to Emacs after several years as an Eclipse refugee. I needed a system for handling my ToDos, and after hearing good things about org-mode I installed Emacs again and gave it a go. And here I am several years later and I pretty much live and breathe Emacs now.
In other words: if you haven’t tried org-mode, you’re probably missing out. Here, have a look at this screencast. It’s short and sweet and you know you want to.