I just found the Omni Group's frameworks they make available for use under a modified MIT License: http://www.omnigroup.com/developer/
The OmniDataObjects framework seems especially useful, since there is no Core Data for the iPhone.
I am new to the Cocoa platform, and don't know what other useful frameworks are out there.
What frameworks do you use in your apps? Did you develop a framework you use in all or your apps?
I've not used it in a real app yet, but the Cocos2D framework is a nice framework for doing mostly 2D animation in OpenGL on the phone - and includes a physics library:
http://code.google.com/p/cocos2d-iphone/
This is under a BSD license so you can use it for non-free applications.
For more 3D oriented stuff, there is SIO2:
http://www.sio2interactive.com/HOME/HOME.html
Which also has a good license and a physics engine.
Of course, it's a good idea to learn a bit of OpenGL just to understand what is really going on - but these frameworks can get your project a long way and do a lot of heavy lifting for you.
There's Touchcode:
TouchCode is made up of:
TouchXML - A document tree XML library with XPath support (based on Cocoa’s NSXMLDocument)
TouchJSON - An extremely fast and memory efficient library for processing and creating JSON data.
TouchSQL - Yet another Objective-C lightweight sqlite wrapper.
Core Plot is a BSD-licensed Mac / iPhone graphing / plotting framework, which aims to be provide drop-in elements for scatter plots, bar charts, etc. It is based on Core Animation and has the same API on both Mac and iPhone.
DrawKit is an extremely powerful BSD-licensed vector illustration framework (currently only for the Mac, due to heavy NSView usage). We've used this as the core for a CAD program we ship with our robotic systems.
Sparkle is a framework for keeping your applications up-to-date. We rely on it for all our Mac-based software, and it's part of many, many Mac applications. I can't recommend it highly enough.
For the more technically inclined, libdc1394 is a cross-platform LGPL library for controlling and accessing video from IIDC Firewire cameras. It lets you get at things on these cameras that QTKit Capture and the like don't.
I would recommend the Google Mac Toolbox. It has some very useful AppKit, UIKit and Foundation extensions. It also includes some great testing aids. It provides support for unit testing AppKit UIs, and UIKit UIs on both the simulator and iPhone.
Not exactly frameworks, but there's a lot of reusable source code for the Mac. I founded a mailing list for people to announce their Mac and iPhone source code.
Of course, things have changed since you originally posted and Core Data is available on iPhone OS 3.0.
(At time of posting) Our CocoaHeads group has aggregated links to over 60 open source projects here: http://cocoaheads.byu.edu/resources/open-source