Here is the open source iphone app list in alphabetical order:
1.ABC 123 –Sequence memorization game.Utilizes Cocos2D.
2.Artifice –Strategy game where you try to get to the other side by moving boxes out of the way.Utilizes Cocos2D.
*3.Battle For Wesnoth –Fantasy themed turn based tactical RPG game available on several platforms and now the iPhone/iPad.
4.Colloquy –Conversion of the most popular Mac IRC client to the iPhone.
5. Countitout-A generic counting app.
6. Diceshaker-Dice rolling simulator designed for role-playing game enthusiasts.
7. Doom Classic-Classic 3D first person shooter.
9. Fosdem-Calendar app for the Fosdem open source conference.
10. Freshbooks –Open Source iPhone app that enables usage of Freshbooks web invoicing software from your iPhone.
11. Gorillas –Classic Worms/iShoot turn based shooter type game converted to iPhone from basic. Utilizes Cocos2D.
12. Go Go Lotto –Open source iPhone app for lotto ticket generation.
13. iStrobe -Turns the iPhone 4 flash into a highly configurable strobe light.
14. Last.fm –Software that enables usage of the Last.fm platform for personal radio stations.
15. Mobilesynth-A monophonic synthesizer designed for live performance.
16. Molecules –Allows you to view 3D models of molecules and manipulate them through touch.
17. Mover –Allows you to transfer stuff from one iPhone to another by “flicking” it to the other device.
18. Natsulion-A basic twitter client converted from mac.
19. NevoChess –A Xiangqi game.
20. NowPlaying –Allows you to check local theater listings, and check rotten tomato ratings.
21. Packlog –Backpack journal client.
22. PlainNote -Simple Open Source Notepad.
23. PocketFlix –Find movies, and manage your Netflix information.
24. Puff Puff –Beautiful underwater 2D game utilizing Cocos2D and Openfeint featuring unique physics based gameplay.
25. reMail –E-mail client featuring ultra-fast search. Removed from app store, but source made available.
26. RobotFindsKitten –Port of a very silly “classic” ASCII game.
27. Sci-15 HPCalc –Calculator app based on classic scientific HP-Calculator.
28. SpaceBubble –Space game featuring core graphics, and accelerometer usage.
29. Star3Map –Augmented reality star and planet charting application.
30. Task Coach –Personal to-do list and task manager.
31. Tubestatus –London train schedule tracker.
32. Tux Rider –iPhone port of the extremely popular, and beautiful 3D Tux Racer game.
33. Tweejump –Platform jumping game inspired by Icy Tower. Utilizes Cocos2D.
34. Tweetee –Enhanced version of the Natsulion Twitter Client.
35. Tweetero –Basic twitter client with image uploading.
36. Twitterfon –Super-fast intuitive twitter client.
37. ViralFire –Unique game where you are a dodging blood cell.
38. Wikihow –A reader app for the popular how to wiki site.
40. WordPress –Client for managing WordPress blogs.
41. Xpilot –Simple massively multiplayer arcade shooter from the early days of the internet
42. YourRights –Pocket database containing a summary of your legal rights.
43. ZBar –A barcode reader open source iphone app.
Check them out if you are working on something similar or think they might have a feature you could use there’s no reason to re-invent the wheel. Always make sure you understand the licenses as many of these open source iPhone apps are GPL and require that you open source your app.