I'm probably late to the party here, but I just ran across these and thought I would share them in case others were not aware they were available. Looks like they could come in handy for a train project or two, but they do require their own app which might be a deterrent? They are just like the ones commonly referenced here for many projects, but can be controlled by wifi and they have them in bluetooth as well. They are also available with more relays on one board as are the others.
Here is a link to one example, there are more if you want to shop around for price. Wifi Relays
