ASIHTTPRequest is an easy to use wrapper around the CFNetwork API that makes some of the more tedious aspects of communicating with web servers easier. It is written in Objective-C and works in both Mac OS X and iPhone applications.

It is suitable performing basic HTTP requests and interacting with REST-based services (GET / POST / PUT / DELETE). The included ASIFormDataRequest subclass makes it easy to submit POST data and files using multipart/form-data.

It provides:

• A straightforward interface for submitting data to and fetching data from webservers
• Download data to memory or directly to a file on disk
• Submit files on local drives as part of POST data, compatible with the HTML file input mechanism
• Stream request bodies directly from disk to the server, to conserve memory
• Resume for partial downloads
• Easy access to request and response HTTP headers
• Progress delegates (NSProgressIndicators and UIProgressViews) to show information about download AND upload progress
• Auto-magic management of upload and download progress indicators for operation queues
• Basic, Digest + NTLM authentication support, credentials are automatically re-used for the duration of a session, and can be stored for later in the Keychain.
• Cookie support
• GZIP support for response data AND request bodies
• [NEW] Experimental support for Amazon S3
• [NEW] Supports manual and autodetected proxies, authenticating proxies, and PAC file autoconfiguration
• Based on NSOperation to make queuing requests and background operation easy
• Comes with a broad range of unit tests

Documentation is available here.