An open source XrmToolBox tool designed to fill a gap where despite something being possible through the API there was no UI for it.
A field within Dataverse has a type and a format - for example a string could be text, a phone number, an email address - see here. You used to only be able to select this at create and it was set that way forever, until Micrsoft updated this and allowed it to be changed across certain data types. This ability to change was released in the API quite some time before the UI caught up - this XrmToolBox bridged that gap and allowed you to change the format of your Dataverse fields as required.
The platform has now caught up and you can do this directly in the maker portal, so this tool is no longer required but the source code is left online for reference.
For more information, please refer my blog post.