Whilst you could already use Bukkit's native event api, I added an event api specificly for ScalaPlugins that aims to be cleaner. Here are its features.

• extend xyz.janboerman.scalaloader.event.Event without having to provide the HandlerList boilerplate (of course you still can if you want).
• implement xyz.janboerman.scalaloader.event.Cancellable without having to provide isCancelled and setCancelled methods (of course you still can if you want).
• A a more type-safe version of PluginManager#registerEvent. The EventExecutor is type-constrained to the event that is being listenend on.
• Access the event bus right from your ScalaPlugin's main class, no need to call #getServer#getPluginManager, just call #getEventBus
• EventBus#callEvent returns a boolean - indicating whether the event is allowed to happen - always true for non-cancellable events.

All ScalaPlugin classes that use xyz.janboerman.scalaloader.event.{Event, Cancellable, EventExecutor} are transformed at class-load time to use their bukkit counterparts. Because of the way this works, JavaPlugins do not get the transformations - meaning they cannot use these types AT ALL, but using subtypes defined in ScalaPlugins will work just fine.

Some example code (also available on github):

That's it, happy Scala coding!