todo.txt

If you know some German, see this article at t3n, otherwise check out the Git for todo.txt. If you want to make use of the todo.txt command-line tool real quick, add this to your .bashrc (Linux) or .bash_profile (Windows/Mac):

PATH=$PATH:"/path/to/todo.sh/folder/"
export TODOTXT_DEFAULT_ACTION=ls
alias t='todo.sh -d /path/to/your/todo.cfg'

You can now use t to add, delete, update tasks.