So you need a control to take input for a messaging/chat application. Easy right? Just use UITextField. What about expanding for multiple lines, or inserting an image from the camera, or showing a character count? I love it when people go to town with getting all of the little details right with a control and it looks like Philipe Fatio has done a great job here.
I've recently written a couple of command line utilities in Objective-C to help with some repetitive tasks and while I did look at using ddcli I ended up just hacking together some very primitive option support myself (which only works as the tools are used internally). This library by Chris Miller will not only parse out short and long form flags but also generate descriptions from the flags, looks like a great way to add proper option support if you are writing a command line tool.
I am a big fan of a well placed NSAssert but in case you aren't you should read this article by Mike Ash which takes you on a thorough trip through the whys and hows of using assertions well.