Leaderboards
Leaderboards are used to display informations about individual players to all players. For example, they can be used to show the number of enemies killed, or the number of quests completed.
Creation
You can create a Leaderboard with the pre-made trigger actions GalaxyEdit offers you, or you can just create your own customized one with the help of Dialogs.
The pre-made trigger actions can be found by searching for "leaderboard" in the search field when creating a new action. They have the advantage of being more explicit as of their use, thus being more user-friendly.
However, creating your Leaderboard with Dialogs has a quite a big advantage as well: you can control pretty much anything about it dynamically. This means you can actually decide of its color, size, elements, and such. It also means you can change any of these at any time during the game (this means you can probably make a flashing Leaderboard if you want).
Examples of Dialog-created Leaderboard are given in the links listed in the "See Also" section.