That software already exists and is called org-mode :)
Some reasons to use org-mode:
* Org-mode is part of Emacs, so you can extend it in Lisp. If you so desired, you could record your weight each morning by sending yourself an email and scheduling an Emacs function... But someone has probably already done that in the 35 years of Emacs' existence. If not, Emacs macros are very easy to write, because they emulate the actions you would take yourself. (See my 9 liner for incrementally searching for keyboard shortcuts: https://github.com/aantn/castle/blob/master/home/.emacs.d/cu...)
* All org files are plain text
* All "items" in org files are part of a foldable hierarchy
* All items can be tagged
* TODOs are really just items whose headline starts with "TODO". Org-mode adds features for toggling, finding, and visualizing them
Sure, but what I need to do then is to write a semi-automated converter which just shoves everything with a clear tag formulation into org-mode and asks me what to do with the rest.
Some reasons to use org-mode:
* Org-mode is part of Emacs, so you can extend it in Lisp. If you so desired, you could record your weight each morning by sending yourself an email and scheduling an Emacs function... But someone has probably already done that in the 35 years of Emacs' existence. If not, Emacs macros are very easy to write, because they emulate the actions you would take yourself. (See my 9 liner for incrementally searching for keyboard shortcuts: https://github.com/aantn/castle/blob/master/home/.emacs.d/cu...)
* All org files are plain text
* All "items" in org files are part of a foldable hierarchy
* All items can be tagged
* TODOs are really just items whose headline starts with "TODO". Org-mode adds features for toggling, finding, and visualizing them
* You can extend org-mode any way you want. For example, I added a DEFER status for my TODO items. (https://github.com/aantn/castle/blob/master/home/.emacs.d/cu...)
* You can scatter your notes across as many files as you want. Org-mode can parse them to build your daily agenda (http://orgmode.org/manual/Agenda-Views.html)
* Org-mode displays formatting without hiding the markup (e.g. everything between two asterisks is bold)
* Org-mode exports to LaTeX, pdf, and html. (Embedded LaTeX is rendered too.)
* Org mode allows awesome links of all kinds (http://orgmode.org/manual/Hyperlinks.html#Hyperlinks)
* Code snippets can be embedded in org-mode and even executed
* Org-mode supports tables with formulas. It also includes a ledger for accounting. (http://orgmode.org/worg/org-contrib/babel/languages/ob-doc-l...)
See my comment below for a discussion on organizing notes and searching in them.