We usually think of model railroading in terms of hardware. However, since the dawn of the computer age, a plethora of model railroad software has been developed - anywhere from realistic train simulation programs, inventory management, layout planning software to sophisticated model railroad operation management. The best article I know of to put all of these different types of model railroad software programs in perspective is on the BYMRR.com website.
Most of these programs are digital, not physical, products and are available for download from the Internet. See the link to the BYMRR.com site for more information.