Building such message activity is very useful for testing because you show the result of a runbook activity in pop up message. The article is written by Stefan Horz and can be found here.
Building our own Message Activity with Orchestrator Integration Toolkit (OIT)
Published by Stanislav Zhelyazkov
Stanislav Zhelyazkov has been working in IT since 2007. Stanislav has started his IT career as a Help Desk Specialist in 2007 while studying Informatics in the University of Ruse. He also worked in HP Enterprise Services (now known as DXC), maintaining large corporate IT infrastructures for clients in Holland, Switzerland and Germany and was involved in a Private Cloud project based on MS Hyper-V and System Center. He was also in the role of Principal Consultant in Lumagate developing and consulting companies on Azure, OMS, management and Private clouds. Currently he is Cloud Infrastructure Engineer at Sentia Denmark. Stanislav is active community member at MSDN forums providing answers on Azure. His blogposts can be found at www.cloudadministrator.net or www.systemcentercentral.com. View all posts by Stanislav Zhelyazkov