Talking of Audiobus, Michael Tyson who developed Audiobus has this week released "The Amazing Audio Engine". This looks to have been in development for a year or so now but has been open sourced this week. Built on top of Core Audio it exposes an easier to use interface to Audio Units, filtering, mixing and all sorts of other stuff. I am no audio developer so I won't pretend to know what I am talking about here but if you are then you should certainly check this out.
Joel Levin with an implementation of the App.net API in Objective-C. It looks to already be a fairly hefty project which may be expected as it supports 100% of the features of the App.net API. If you were looking for an MGTwitterEngine for App.net then this may be your answer.
Javier Soto with a category on NSError to include a stack trace of the creation of every NSError along with the error itself. One for the debugging toolbox.
More debugging goodness from Conrad Kramer with a small category which adds return and parameter type information when logging out a block, useful. Looking through the source was also an good introduction to some of the metadata available on a block as well.