RegexKit is an open-source Objective-C framework for regular expressions which wraps PCRE, with Leopard and 64-bit support.
RegexKit seamlessly adds regular expression support to all NSArray, NSData, NSDictionary, NSSet, and NSString Foundation objects with a rich set of Objective-C category additions. It's tuned for high performance, including such features as compiler regex caching, safe multi-threading, minimal use of heap memory, and use of OS X's Core Foundation. In addition, it has complete support for Leopard's Garbage Collection feature, and includes several instruments for use with Instruments.
The developer also provides a RegexKitLite framework, which provides a small subset of RegexKit's
NSString methods for performing various regular expression tasks. RegexKitLite uses the ICU library that ships with the operating system, whereas RegexKit ships with a PCRE library. This means that using RegexKitLite will add only a couple kilobytes of overhead in a compiled application, while RegexKit has the potential to add several megabytes to the final app size.