DevTodo is a small command line application for maintaining lists of tasks. It stores tasks hierarchically, with each task given one of five priority levels. Data is stored as XML, so various XSLT templates can be executed on the XML to convert it into different formats (eg. HTML).
Data is stored in a file named .todo in the current directory. Depending on the setting of backup in your configuration file, there may also be files named .todo.1, .todo.2, etc.
The change log is also of interest for highlighting the newest features and bug fixes.
DevTodo is available in most Unixes, but you can also download the source directly from the bottom of this page.