A new application is now available in Cydia called Backgrounder, which leaves applications running even after you hit the home button. Traditionally, the iPhone will terminate an application after the home button is depressed to return to the home screen. Backgrounder, as the name implies, lets applications run in the background allowing you to return to them in the future. This ability is great for applications such as MobileCase for downloading podcasts in the background while you surf Safari or check Mail, or for instant messaging applications to continue to run like BeeJive. The downside is that your battery life will be quickly depleted.
» Backgrounder Adds True Multi-Tasking

Yesterday apple posted the second beta of the iPhone 2.1 software to developers for testing. Some developers are reporting they have since recieved the tools from apple to create background apps. Apple told us it would not officially be released to devs until September. For a more detailed explanation of how the push notification works read on. » Apple seeds some developers tools for making background-notification apps.