TileMill Connect is set to ship in the coming weeks as part of the latest Arc2Earth Sync, an incredible plugin that bridges your desktop ArcGIS tools to geospacial cloud services, including MapBox.
Adding Arc2Earth Sync to your existing ArcGIS toolset means you don’t need to learn a whole new toolset to publish beautiful maps on the web. ArcGIS remains a powerful part of the traditional map making workflow, providing the infrastructure for data collection, management, and analysis. With TileMill Connect, you can extend that workflow to include breakthrough map design and publishing from MapBox. To start publishing your ArcGIS maps online get Arc2Earth and sign up for Sync.