Today we announced a new open source project called Update Engine. Update Engine is a framework to help developers keep their software up-to-date. See the Google Mac blog post for a quick overview and a link to some demo movies explaining Update Engine [and yes, I knew I sounded like kermit when I recorded the video—I even told my wife but she didn't think so... oh well ;-)].
Also, we did not build Update Engine to compete with Sparkle. We built Update Engine to solve different problems. If you're interested, here's my reply about this in the Google Group for the project.