The RFID UHF Toolkit is no longer available. However, there are two tools compatible with Workabout Pro 4 that provide the same essential functionality:
EMDK for .Net Toolkit provides developers with the tools necessary to create C# and VB.NET managed applications. These tools include class libraries, sample applications, and associated documentation. EMDK for .NET allows Microsoft® .NET Compact Framework developers to programmatically access the enterprise mobility features on the devices. This developer kit is designed for use with Visual Studio 2005 and Visual Studio 2008.