Aquatic Prime

If you are looking for a free registration method for your applications take a look at AquaticPrime framework.

Software update framework

If you are looking for a free software update framework take a look at sparkle by Andy Matuschak.

Per-object ordered relationships using Core Data

For all people interested in how to make ordered relationships possible in CoreData i recommend to read a post by Brian Webster (Fat Cat Software). It is a good starting point.