Rovio:

Some of you may have noticed a new feature in your Rovio games called Rovio Account. Our fans have been asking for a way to play their game on different phones or tablets without losing their progress when changing the device. This is exactly what Rovio Account lets you do!

Another developer who ends up shipping an in-house implementation that doesn’t rely on iCloud or Game Center. For Rovio, I guess that cross-platform syncing was also an important factor to consider.

More details are available in the FAQ.