[jph]

Even better for developers: Todo.txt http://todotxt.com/

Free, open, plain text, with lots of optional tools for the command line and also mobile.

And for more power, emacs org mode is amazing.

[manojlds]

PowerShell implementation for those on Windows - https://github.com/manojlds/todo.ps1

[kennywinker]

I just paired todo.txt with this technique by adding:

    cat $HOME/Dropbox/todo/todo.txt

to my .bashrc file.

[brink]

| Free

Not completely. The associated Android app I just bought is $2. Though it's still not much.

[ing33k]

we can compile it from the source https://github.com/ginatrapani/todo.txt-android ( but I also bought it )

[mikevm]

I prefer a hierarchical TODO list a-la MLO: http://www.mylifeorganized.net/ But that one is a rather expensive since it requires a cloud subscription if you want to sync it across all of your devices.

[rjzzleep]

not sure if there's an ios version(there is an android app), but if you don't edit the todo.txt in a normal editor normally you might want to take a look at taskwarrior http://taskwarrior.org/projects/show/taskwarrior

it has import scripts from several things including todo.sh, and several export scripts including ical. there's a decent third party android app if you really want that.

it has task undo support, and generally seems much more powerful than todo.sh.

obviously main advantage of todo.sh is that you can edit the file in a plain text editor.

[soupboy]

+1 for todo.txt. I used it extensively all of last year and saw an immense boost in productivity. Best part is the ability to write plugins.