4X games - that is, space strategy games - have been enjoying a renaissance of late, and the iOS App Store has its own seminal masterpiece in the shape of Ascendancy. It's an incredibly deep and infinitely replayable tactical experience, though the complex interface requires a fair bit of perseverance to master. Running a space empire isn't easy, after all. But it is cheap as chips, thanks to a weekend sale that will save you 80%. Ascendancy demands your attention, especially considering the £3+ major saving.