1. CrystalSky is a Spigot plugin that brings a rank shop system to your Minecraft server. With CrystalSky, you can offer your players the ability to purchase special ranks using the in-game economy.

2. The main features of the plugin include:

- Utilization of the Vault API for easy management of the server's economy. You can connect CrystalSky to your preferred economy management plugin using the Vault API.

- Creation of a custom Graphical User Interface (GUI) for the rank shop. Players can access the shop through a specific command and navigate a user-friendly interface to view available ranks.

- Configuration of rank prices and materials through a configuration file. You can set the prices for each rank and define the materials used to visually represent the ranks in the shop.

- Listening to player events such as inventory clicks. CrystalSky handles player interactions with the shop, allowing players to select and purchase desired ranks.

- The "/grade" command provides access to the rank shop and allows players to buy ranks. Players can use this command to open the rank shop and view available ranks for purchase.

- Automatic assignment of ranks to players with updated display names. When a player purchases a rank, CrystalSky automatically updates the assigned rank for the player and their displayed name in the game.

- Integration with the player tab list to display ranks. Assigned ranks are displayed in the player list, visually distinguishing players with special ranks.