MacIndie

If you had to describe the basic functions you would expect all MacOSX apps to provide, which would they be?     I’m not referring to the most basic, capabilities such as  the fact all apps should support (where appropriate) cut/copy/paste/unlimited-undo and the ability to work with multiple documents .. Think about something a little [...]

URL: http://sparkle.andymatuschak.org/
Description: Sparkle is perhaps the most common yet most invisible piece of Open Source Mac code in use today.  Almost every major indie software package uses Sparkle by Andy Matuschak (with contributions by dozens of others) to check for and install software updates.  It provides a simple, direct and customizable interface that allows [...]

URL: http://code.google.com/p/google-toolbox-for-mac/
The Google toolbox for Mac is a collection of open source code for the Mac and iPhone. It includes several different modules including:

Objective-C Address book API for iPhone.
A large number of Foundation and AppKit extensions and categories
Debugging utilities
Spotlight importers useful for developers
A complete and extremely capable unit testing harness
A set of XCode configs useful [...]