Any recommendation of software for keeping a mathematical diary? I believe that it might be a good idea to keep a personal mathematical diary, recording your readings, questions, thoughts, research ideas, etc. Surely one can choose to keep paper-based journals, but electronic ones are easier to store and manage. 
I am aware that there are numerous software for journal keeping, some of which are free of charge (and good!). But I also noticed that (almost?) all of them do not work well with mathematics. It may not be easy to write a simple formula such as $A=\pi r^2$, let alone a commutative diagram, or more complicated stuffs.
So I wonder if anyone knows any diary-keeping software (free ones preferred) that works well with mathematics; namely, it is very easy to input mathematical expressions, as one would do with $\LaTeX$.  
 A: Wordpress has a MathJax plugin and is easy to manage and you can sign up for free. If you want to keep everything private, it is easy to set the visibility of your posts/entries to private.
A: Tim Gowers recommended TiddlySpace. It has a MathJax plugin.
I tried it and found it easy to get started, but then I didn't keep using it.  But it seems to me like it would be good for mathematical journaling.
A: This is essentially an extension of Arkamis' answer. If you want something that doesn't require the internet, you could install Apache+PHP+MySql on your own computer, which is not hard if you read some tutorials. Then you can install Wordpress locally with MathJax and have it start whenever you open your browser. I use this system and it's the first note-taking system that I have actually stuck with. 
The advantages of this are that you can easily define your own LaTeX macros in a separate file on the "server" and you can access the local Wordpress without the internet. It's great for Live TeXing talks and keeping other notes. 
Moreover, it's looks better than most of the note-taking applications I've used and can be heavily customised. For instance, you can install Wordpress plugins (to make table of contents for instance, format code, etc) and other open-source webapps (calendar to keep track of talks maybe) to truly customise it for your needs.
