Chillingo's top-notch physics-puzzler Feed Me Oil is currently available free of charge, marking the first time the game's been discounted since its June 2011 release.
Taking aesthetic inspiration from 2D Boy's superb World of Goo, Feed Me Oil has you placing barriers and objects in order to steer liquid oil around each of its surreal stages.
'Why am I doing that?' you might reasonably ask. Well, it's because each level contains a nightmarish monster, and it's your job to feed the beastie its liquid lunch.
If that sounds odd, that's probably because Feed Me Oil is an odd game, but it's also smart, challenging, and blessed with some fantastically fluid physics.
It may wear its inspirations on its sleeve, but Feed Me Oil's sheer mechanical ingenuity earned it a glittering AppSpy 5/5 in our review.
There's no word on how long this one will remain an App Store freebie, so our advice would be to pick up this puzzler for nowt while you can.