Looking for a USB/PCI controller that can replace a physical switch
Check these:


Single Channel USB relay controller
4 Channel USB relay controller


BUT! Don't forget to check if the provided relays are suited to your application voltage/power. If not you should couple a suitable relay.

I suppose you'll be able to load the DLL in your .net application and connect to them right away. Otherwise you could end up writing your own driver (usually these devices are listed in your OS as serial port devices making it fairly easy to connect to them directly and use the command set they provide).



Googling for "USB IO kit" or "USB relay" will give you many more options.