Org-mode is a note taking tool to be used with Emacs. It is geared towards authoring documents, taking note, keeping todo lists and planning projects, all in a simple text format.
Pro Basic spreadsheet functionality
Org-mode has some basic spreadsheet functionality. Other than auto-formatting ASCII tables (a notoriously annoying problem), it also has support for LISP-like syntax to define equations or any other functionality that can be achieved through spreadsheets.