Windows 95/NT
Programming for Windows 95/NT's 32 bit Graphical User Interface (GUI) produces a much more solid product then previous Windows environments. The 32 bit environment is considerably more stable then it's 3.1x counterpart for both development and just everyday use. We use both Visual C++ (with Assembler) and Visual Basic to development for this environment.

Windows 3.1x
Although the 32 bit environment is better there are still a lot of Windows 3.1x 16 bit GUI users out there, so it behooves us to continue to offer our services to the old operating environments. As people and companies upgrade their software, after awhile this tends to require them to purchase new hardware (software drives hardware purchasing). Since new computers come shipped with Windows 95, more and more people will be switching over to the newer operating environment. We use both Visual C++ (with Assembler) and Visual Basic to development for this environment also. Not only have we written user programs for Windows 3.1x, we have also written Windows device drivers to communicate with both standard devices and special equipment.

DOS
Yes, some are still in DOS, though that number is dwindling fast, we still offer programming in Visual C++ and Assembler. We have done a wide variety of things in DOS including device drivers, boot records, and terminate-and-stay-resident (TSR) programs.