TFS Aggregator is an extension for Team Foundation Server (TFS) and Visual Studio Team Services (VSTS) that enables running custom scripts when Work Items change, allowing dynamic calculation of field values and more.
This Web Service version, for VSTS or TFS 2015 and later. You have to setup an hosting environment (basically an IIS Web Site) and it runs out-of the TFS process. The Web Service is the only option for Visual Studio Team Services (VSTS).
If you have TFS on-premise, you can instead use the Server Plugin, for TFS 2013 Update 2 up to TFS 2017 Update 1.
Go to the project's site https://tfsaggregator.github.io/ for more information and downloads.
What's new in v2.3 (beta)
Some uses cases