This XCode project is intended to demonstrate the usage of custom UITableViewCells as kind of combo boxes (as known from [X]HTML) or dropdown boxes. The code used to provide this is just a rough prototype and in no way production-ready, but it can give you an idea of how you might realize this behaviour in your own iOS projects.
This class allows you to use a UILabel with NSAttributedStrings, in order to display styled text with mixed style (mixed fonts, color, size, ...) in a unique label. It can also detect links, add custom links, use basic markup to create your NSAttributedStrings easily (instead of lots of lines of code), and much more. Use it as a drop-in replacement for any of your UILabel. Compatible with iOS4.3 and later.
Chameleon is a port of Apple's UIKit (and some minimal related frameworks) to Mac OS X. It is meant to be as much of a drop-in replacement for the real UIKit as possible. It also adapts some iOS user interface conventions to the Mac (such as UIAlertView being represented by NSAlert) so that apps built using Chameleon have as much chance as possible of feeling at home on the desktop with relatively little porting effort. Chameleon requires OS X 10.6 or higher. Apps built with it have been proven to be acceptable to Apple for the Mac App Store. Chameleon was first built by The Iconfactory to unify the codebase of Twitterrific for both Mac and iOS.