Add-in Express for Office and .NET - Version 2010 Add-in Express is all-in-one platform for developing any types of Office extensibility projects. You use vi sual desi gners instead of error-prone coding to create powerful COM add-ins, smart tags, RTD servers and Excel UDFs fo r all available Microsoft Office ve rs i ons, from 2000 to 2010 . Using Add-in Express you can cre