Add-ons for Plugins

Good evening everyone,
I am creating a plugin that could have different add ons, which would be different features that do not need to be there and don't need to be included in the actual Plugin, however I would like them to be able to communicate between the two.
For example, one of the Plugins could have a currency involved while the other could be ways to spend this currency so they need to interact in real time not just updating the save file from both plugins or every time anything changes the entire database would need to be saved and restored.
Any ideas or pointers in the right direction would be great.
I'm pretty new to plugin development however I'm very experienced (to the point of fluency) in Java so nothing is off the table in terms of difficulty.
thanks

 

durpnhard Like an API? Like Vault?

 

Can I create my API without needing to bundle the API jar along with it?

Edit: this would make splitting the different plugins into different jars if so

 

You can make an API as a plugin and have other plugins depend on it. Although if you can also have addons specifically for your plugin such as other jars that go in say "/your-plugin-name/addons/" that will be loaded into your plugin dynamically (similar to the way plugins work with craftbukkit).