Microsoft has made available its Microsoft Robotics Developer Studio 2008 R3 or RDS, free to all.
The previous versions of RDS had multiple releases: one free but with limited features and another a full commercial version which one neede to purchase.
Microsoft Robotics Developer Studio 2008 R3 from Mictrosoft Robotics, is a .NET based programming environment for building robotics applications.
In addition to providing support for Microsoft Visual Studio 2010, Microsoft Robotics Developer Studio 2008 R3 provides a Visual Programming Language (VPL) which allows developers to create applications simply by dragging and dropping components onto a canvas and wiring them together.
It can be used by both professional and non-professional developers as well as hobbyists and you can download it from the Microsoft Download Center.