In Sky, players explore a once-prosperous kingdom using a cape that allows them to fly. The in-game world consists of seven unique realms, each with a variety of areas to explore, and a theme representing different stages of life. There is also Home, a small island which serves as the world hub and the starting point for the player. Throughout the world, players encounter "spirits" that allow them to unlock items in return for in-game currency, and "children of light" that give players "winged light." When a player has collected enough winged light, their cape level goes up, allowing them to fly farther.
The game places heavy focus on social mechanics. Players are able to meet and befriend one another, and can unlock new abilities such as chat and sending gifts as their friendship grows. There are also many cosmetic items to collect including capes, masks, hairstyles, hats, pants, playable musical instruments, expressions, and more. These items can be obtained using in-game currency or, in some cases, purchased with real money. Some cosmetics are only available to select players, such as the original beta cape, only available to those who played the beta version prior to the full release of the game.
Source: Wikipedia, "[en.wikipedia.org/wiki/Sky_%28video_game%29 Sky (video game)]", available under the CC-BY-SA License.