A few super popular games on the App Store have basically helped spawn the "time management" genre. Games like Diner Dash and Sally's Spa pioneered the genre, and Sally's Salon follows in that tradition. The game tasks you with moving cashier, stylist, and masseuse Sally around her salon, where she has to take care of customers as quickly as possible. Sally's Salon is stylized for girls, with lots of pink and sparkles to go with the theme of a beauty salon, but the gameplay actually gets quite hardcore. It ramps up well as the customers quickly move in and through the store, and you try to make as much money as possible.
The app recently got a free upgrade to the "Luxury Edition," adding new salon locations, updated graphics and controls, and better visuals. As I write this, the app is just US$0.99, but even at the regular price of $2.99, it's an excellently polished game with very solid gameplay. If you're an old hand at the time management genre, or if you just want an excellent introduction to the process, Sally's Salon is a great way to dive right in.