Hi there,
I'm building my own wallet app for Mac and iOS. The app will be open source when it's ready. Before that, to do things more efficiently, I open source CoreBitcoin, a clean implementation of Bitcoin protocol in Objective-C (with bits of OpenSSL).
The library is not complete yet, but with a help of volunteers I may finish it faster. It is also meant to be cleaner and easier to read by newbies than Satoshi code, bitcoin-ruby or libbitcoin. I try to make every step explicit, documented and simple.
https://github.com/oleganza/CoreBitcoinFeedback is welcome. Thanks.