XSL-FO is similar to HTML in that it allows documents to be created in a markup language. The fundamental difference between the two is that XSL-FO is intended for creating paged, printable documents, whilst HTML is more suited to onscreen documents.
FO.NET processes XML documents that conform to the XSL-FO specification and produces Adobe PDF documents.
FO.NET has been written for the Microsoft .NET Framework and is suitable for use from any .NET compatible language such as C#, VB.NET or C#.