Android (4.0+): HomeFlip won't replace your default app launcher, but it comes in handy when switching between apps. Tap the home button once to bring up a custom list of your favourite apps overlaid on top of the one you're using. Tap home again to go to your default launcher.
Think of HomeFlip as a middle-man app launcher -- one that only has icons for the apps you want to get to quickly. On most Android phones, you can only see the apps you have used recently. HomeFlip lets you customise the apps it displays when you tap the home button, so you can quickly jump from app to app. As we mentioned above, it doesn't replace the default launcher -- tap the home button twice and you will drop back to your home screen.
HomeFlip is the work of XDA developer id0x12345, who has promised to keep the app free and ad-free forever. He's also planning to add swipe-to-activate as a feature in an upcoming release, much like previously mentioned SwipePad. You can check out his dev blog here (complete with a link to the APK for people who can't get it at Google Play) and the user guide here.