Reiner Knizia's Ra is the universal iOS adaptation of the popular European-style board game Ra (by German game-design legend Reiner Knizia), a fast-paced game of bidding and building that's nominally about achieving fame in ancient Egypt.
Ra is a pure auction game, with simple rules and a shallow learning curve once you get its basic flow. It's always easier to learn a board game from somebody who knows how to play it, but the app does include complete rules and a good bit of in-game help for novices.
Ra is divided--and scored--in three separate stages ("epochs" of Egyptian history), and players bid competitively for sets of tiles, which illustrate various gods, gold, monuments, pharaohs, and the like. Different tiles have a different impact on each player's score, so you need to know what a set of tiles is worth to you, what it's worth to your opponents, and how that might change over the course of an epoch. This iOS version does a good job of translating the game's central auction dynamic (complete with its brinksmanship and schadenfreude)--and it even makes the auctions more fluid, by eliminating some of the bookkeeping of the original, with features like scoring summaries and the ability to click on any tile to see its rules and scoring details (including how many of a given type of tile remain in play).
The animated interface (with optional Egyptian background music and sound effects) looks very much like the Ra board game, with a couple of improvements: a small sundial shows you how many Ra tiles have been drawn (which lets you know when the epoch will end), and it's always easy to see what tiles and bidding tokens each player is holding.
Ra supports from two to five players, with any mix of humans (for pass-and-play multiplayer) and AIs (with eight different AI opponents), and you can also play online through OpenFeint, although you'll probably have more luck finding games with people you know than random pickups. If you're new to Ra, the game can be a bit overwhelming--but it's a classic for a reason, and the app version will reward your patience. If you're already a Ra fan, you'll definitely enjoy this faithful adaptation (and it will give you a chance to hone your skills in solo play).