This project provides a component that you can add to your iPhone application to access all basic features of Google Maps (similar to Android’s MapView). It uses a UIWebView in the background to load the HTML/Javascript version of Google Maps, and offers a set of Objective-C methods that mimic a subset of the original Javascript methods for controlling the map. It currently supports setting the center location, and zooming & panning using the touch interface.
iTwtr is a simple web-based Twitter client specifically designed for the iPhone. It was created by Dan Phiffer. iTwtr is open source, so you can hack on the code and run it on your own server.
WordPress for iPhone is the first Open Source app that lets you write posts, upload photos, and edit your WordPress blog from your iPhone or iPod Touch. With support for both WordPress.com and self-hosted WordPress (2.5.1 or higher), users of all experience levels can get going in seconds.
ZXing (pronounced “zebra crossing”) is an open-source, multi-format 1D/2D barcode reader library implemented in Java. The goal is to support decoding of QR Codes, Data Matrix, and the UPC family of 1D barcodes. Working clients for Android, Java ME , iPhone, and BlackBerry devices will be provided.