Access.NET is a tool that converts MS Access projects into .NET solutions using C#. It converts Access databases to SQL Server databases and Access forms to equivalent Windows forms. The tool aims to allow developers to build on existing Access projects using .NET technologies. Key challenges in developing the tool include mapping Access controls to .NET equivalents, handling calculations, and compiling VBA code to VB.NET code. The generated .NET solution contains modules like a forms connector and data access layer to manage the converted forms and database access.