Dyalog allows you to not only make full use of Microsoft.Net framework components, but to deploy your APL code as .Net assemblies that can be used by any other .Net programming language. You can also write Classes in Dyalog APL which derive from classes written in other .Net languages, and vice versa. For example, implementing an ASP.NET web page is done by writing APL classes which derive from ASP.NET base classes.
The DotNet Interface Guide describes how to use and provide .Net components. It is avalible from the Documentation Centre (Help|Documentation Centre in v12.x and on line at http://www.dyalog.com/documentation).