There's a great Macintosh app called TaskPaper as well as an open source web-based implementation called TaskPaper.web. My version is another web-based implementation but with the guts written in Python.
The main benefit for me was that unlike TaskPaper.web, TaskPython.web is able to run natively on my jailbroken iPhone with Python and a web server installed.
It works on a normal web server too, and hopefully I'll be able to write a syncing function between the two.
I've only tested it with Firefox 3 and the iPhone Safari web browser, but since the html isn't too wacky, I assume other browsers shouldn't have too much of a problem with it.
Make sure you have Python installed on whatever webserver you're using. If you are using it on an iPhone, it must also be running a webserver like lighttpd or Apache.
Simply upload the python script(taskpythonweb.py) and task file(todo.txt) to your webserver and make sure to change their permissions on the file to 755.
Then just point your web browser to the Python file and it should work from there.
The look of the app can be changed through the css stylings embedded in the html.
These details are provided for information only. No information here is legal advice and should not be used as such.