Programming to interfaces is at the core of flexible structure.

There are thousands of to-do list apps out there, in part because no system works perfectly for everyone. I’m not going to say todo.txt is the exception, and that it will work for everyone, because that would be crazy. But todo.txt is the most flexible tool I’ve come across. In part, this is because of the sheer number of clients available, but also because the simplicity lends itself to improvisation.