SharePoint features are an incredibly useful way to deploy chunks of functionality to web sites.  Although they can be difficult to grok at first, once you do, they make a lot of sense!  Scot Hillier, a very well known SharePoint expert has begun a CodePlex project titled SharePoint Features, which aims to provide some extra functionality to SharePoint.  He's kicked off the project by contributing some really cool stuff, including a Debugging Feature, a Log Viewer Feature, and a Theme Changer feature.  He's also got loads more up there!  Have a favorite feature you've built?  Contribute!

I haven't checked out what license they are released under, but they're worth checking out!