With a few notable exceptions, most Mac software has really lame update functionality. Programs will usually just tell you that there's a new version available, point you at the web site, and make you do the rest.
Sparkle is a module that developers can stick in their Cocoa applications (five-step install!) to get instant self-update functionality. By that, I mean that your app will be able to update itself, not just check for new versions: it'll read the update information from an appcast on your server, download, extract, install, restart, and even offer to show the users release notes before they decide if they want to update.
It's free, it's easy, and it'll make using a Mac better for everyone, so go for it!
What's new in this version:
The most important things to know: The 10.3 support is untested at best; sketchy at worst. Test with it thoroughly before you use it. Sparkle now asks for permission to update on second launch; don't be surprised at that. You can change that behavior with a delegate method; read SUUpdater.h for more info. We no longer distinguish between "check on startup" and "scheduled updates"; everything is scheduled, with the default being every day. The te...