Adobe CEP Extensions
CEP or Common Extensibility Platform is the name of the platform used to create third-party extensions for Adobe Creative Cloud apps, it allows for the creation of custom panels and modal dialogs that can interact with the active document and interface with other services both offline and online and provide integrations with other applications. The opportunities are near endless. I have developed and released extensions for Adobe Photoshop CC, Audition CC and Illustrator CC. But i am able to develop extensions for any Adobe app with support for CEP.
Adobe Extendscript Scripts
Adobe Extendscript is a custom programming language developed by Adobe for use in Adobe Apps for automating repetitive tasks and creating custom tools and utilities for specific workflows. Most Adobe apps support extendscript unlike CEP. While most of my experience in Extendscript comes from CEP extensions, i am also able to create stand-alone scripts.
Adobe XD Plugins
Adobe Experience Design is soon to receive advanced plugin support, having worked with Adobe on this plugin API i have plenty of knowledge on creating plugins for Adobe XD.