Choose your development style for managed code - Create and deploy plug-ins or custom workflow activities

 From MSDN Web Site i took this:

https://msdn.microsoft.com/en-us/library/jj602917.aspx#create_and_deploy_plugins 

The following table lists the choices you have for writing and deploying plug-ins and custom workflow activities. 

  

Tool	Description and usage	More information
Plug-in and Custom Workflow Activity classes  Plug-in Registration Tool	The plug-in and custom workflow activity classes allow you to create event handlers to perform custom business logic that you can integrate with Microsoft Dynamics CRM to modify or augment the standard behavior of the platform.  By using these classes directly, your code will not contain any helper code provided in the Developer Toolkit.  If you write plug-ins and custom workflow activities from scratch, you must use the Plug-in Registration Tool to register them. This tool provides a graphical user interface and supports registering plug-ins and custom workflow activities with Microsoft Dynamics CRM.  Use this method if you:  Understand how to use the plug-in and custom activity classes.  Don't want extra library code auto-generated and placed in your code files.  Don't mind using an external tool and the web application to register and package custom code assemblies.	Plug-in development  Custom workflow activities (workflow assemblies)  Register and Deploy Plug-Ins  Walkthrough: Register a plug-in using the plug-in registration tool

Hop it helps.