That's going to place a severe restriction on which system you can use, because very few of them have a computer interface.
Digitrax has already been mentioned, and I believe that the NCE system and EasyDCC from CVP Products can also be computer controlled.
For my G-scale trains, I use the AirWire900 radio-controlled, battery-powered system.
When I run trains, I want to be in control instead of trusting a computer to do everything, so I have never explored interconnecting a computer and DCC system (I have 3 different systems; AirWire900 for G-scale; NCE wireless for my home HO layout, and EasyDCC wireless at the HO scale club layout).
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