Denizen's Project Layout
Denizen is a plugin for Minecraft servers that parses and interprets a scripting language called DenizenScript. The most popular implementation of Denizen is the Spigot implementation, which is the jar you've most likely downloaded many times. At the time of writing, it is the only maintained implementation.
Any Denizen implementation depends on DenizenCore, which is the main set of tools that powers every language feature. It includes all content that isn't implementation-specific, such as basic ElementTag manipulation and data script containers.
Support for other plugins within Denizen scripts is provided by Depenizen. It uses the tools provided by both DenizenCore and Denizen to interact with external APIs. This is also the case for dDiscordBot, although it focuses on a single API (that being Discord).
Unless you're going to be working with core language features, most of your code will be recognizably similar, and you can find numerous examples throughout these projects for each type of contribution.