Workflow - Plugins
Symantec 
Workflow Manager has a number of Plugins available from install.
Workflow - Plugins - Generate Business Model
The 'Generate Business Model' Plugin allows you to add a custom Model to your Project which allows a process to be documented, this is not going to produce any code but is a great place to inform Developers who you wish the process to be work.
Workflow - Component - Developer Guide - WindowsForm
In this Article I'm going to explain how to add a Form to your Plugin to allow user interaction.
Workflow - Plugin - Developer Guide - Inspecting
In this Article I'm going to explain how to inspect other Plugins to learn how to implement items that aren't in the Developer Guide PDF.
Workflow - Plugin - Developer Guide - Simple Plugin
In this Article I'm going to explain how to create a simple Plugin with the basic properties and show some infomation about the current Project.
Workflow - Plugin - Developer Guide - Setup
In this Article I'm going to explain how setup your environment for creating a Plugin.
Workflow - Plugin - Developer Guide
In this set of Articles I'm going to explain how to create a Plugin for use within 
Workflow.
Workflow ServiceDesk - Projects
Here is a list of Workflow/ServiceDesk Projects not included in the base install of WF/SD.
Workflow - REST Generator
I've written a number of Articles on the Workflow REST Generator, here is a list: