Overview Q & A Rating & Review 
TFS Aggregator is an extension for Team Foundation Server (TFS) and Azure DevOps Server (VSTS) that enables running custom scripts when Work Items change, allowing dynamic calculation of field values and more.
Deprecation notice 
Azure DevOps Server is deprecating the old work item APIs . They are likely not going to be removed any time soon, but we can't keep supporting this plugin version forever.
Our recomendation is to migrate to aggregator-cli which can now be hosted on Azure Functions or in Docker .
We won't do any major investment in this Plugin version and our bandwidth for support is limited.
 
The Server Plugin  , for TFS 2013 Update 2 up to Azure DevOps Server 2020, runs in-process of your on-premise Application Tier and is the most performing option. The Application Tier takes care of insulating from crashes in the plugin.
Go to the project's site https://tfsaggregator.github.io/  for more information and downloads.
What's new in v2.6 
Adds support for Azure Devops Server 2020 beta, RC and RTW. 
 
What's new in v2.5 
Adds support for Azure DevOps Server 2019.0, 2019.0.1, 2019.1RC1, 2019.1RC1, 2019.1 
Adds support for TFS 2018.2 and 2018.3 
 
What's new in v2.4 
Added support for TFS 2015.4.1 
Added support for TFS 2017.0.1 
Added support for TFS 2017.1 
Added support for TFS 2017.2 
Added support for TFS 2017.3 
Added support for TFS 2017.3.1 
Added support for TFS 2018 
Added support for TFS 2018.1 RC 
Added support for TFS 2018.1 
Added support for TFS 2018.2 
Fixes TemplateScope in TFS 2017 update 2 and higher 
Added text to installer explaining the 2017u2 version works with 2017u3 as well 
Added text to installer explaining the 2018 version works with 2018u1 as well 
Reading and removal of Work item Links self.WorkItemLinks self.RemoveWorkItemLink 
Global List editing with AddItemToGlobalList and RemoveItemFromGlobalList 
Startup logging controlled by configuration file 
New code layout, contributors are urged to read Source Code 
Support for work-item-deleted event 
 
What's new in v2.1.1 
Fixes important bug causing very high CPU usage (see #160 ). 
 
What's new in v2.2 
Support for TFS 2017 
Macro snippets and Functions for Rules and make code more modular 
Ability to specify server URL 
Support for multiple workitem Ids in Console application (issue #178 ) 
Ability to Send email from Rules 
Migrated CI build from AppVeyor to VSTS 
Use of GitVersion to manage Semantic Versioning  
 
Some uses cases 
Update the state of a Bug, PBI (or any parent) to "In Progress" when a child gets moved to "In Progress" 
Update the state of a Bug, PBI (or any parent) to "Done" when all children get moved to "Done" or "Removed" 
Update the "Work Remaining" on a Bug, PBI, etc with the sum of all the Task's "Work Remaining". 
Update the "Work Remaining" on a Sprint with the sum of all the "Work Remaining" of its grandchildren (i.e. tasks of the PBIs and Bugs in the Sprint). 
Sum up totals on a single work item (i.e. Dev Estimate + Test Estimate = Total Estimate)