You can browse the full library above, or use this short summary of select samples.
Sample 1 is a good demo of how we get a less experienced developer quickly up to speed on basics like organising project files, writing better commit messages and taking compiler warnings seriously.
Sample 2 takes on issues with an App Delegate that's doing too many things, it's also a good demo for how reviews follow up on issues.
Other reviews you may find interesting are about Threading or Architecture. There are also quick notes about things like Magic Numbers, something which constantly frustrates us when trying to tweak someone else's animation code.