HJCache is library for asynchronous download of images and other data over the net, and for sharing and caching them. Its for iPhone / iOS, it works with data other than images too, and its free. The library is designed to make it easy to make fast scrolling table views (for example) that contain imaged loaded from URLs. Eg a twitter app that shows the profile pic for each post in each table cell.

More info here: http://www.markj.net/hjcache-iphone-image-cache/

HJCache was developed as 'HJ Managed Object' hence the 'MO' in the class names, but we renamed it HJCache because most people who need it probably start off looking for caching libraries.