Android: MinimalLock keeps your lock screen clean and clutter-free with a gesture-based approach. You can perform tasks with swipes and get quick access to missed calls and incoming text messages.
There are a lot of custom lock screen apps out there, but MinimalLock emphasises minimalism over customisability. You don't have to deal with lots of sliders and other random icons cluttering up your screen. You can unlock your phone and change music tracks with just a few gestures, display your network and battery info at the bottom, or choose to have nothing there at all.
The really handy thing about MinimalLock is the fact that it shows notifications for missed calls and text messages on the lock screen in the form of contact photos. So you can see who's trying to contact you right at a glance, without even unlocking your phone. Grab the pro version and you can have notifications for other services too, such as Google Talk, Gmail, Twitter and Facebook. Note that you'll want to set your gestures in the app's settings before you lock your phone, otherwise you may not be able to get back in!
MinimalLock is a free download for Android phones, with a $2.99 pro version available.