Since the App Store opened its virtual doors, we've seen a lot of "micro" versions of larger genres, including platformers and RPGs. The iPhone lends itself to smaller, quicker experiences, and so a lot of developers have boiled down some very large game styles into much smaller forms. Slayin is essentially a very boiled down fantasy role-playing game, and it's probably one of the most charming games of this type I've ever seen.
The idea is ingenious. You play as a hero who constantly moving back and forth across the screen, facing endless waves of enemies and bosses. There's just one rule: Anything that touches your outstretched sword gets hurt, and anything that touches you hurts you. There are buttons to switch your direction and