Free. No signing up, no card.
Get it on Google PlayFor an Android phone or tabletGet it on the Microsoft StoreFor a Windows computerThe same program on both. One device is free; connecting them is BOS Online.
Open the app. If you have a code from the shop owner, put it in on the first screen. If not, just start.
The store keeps it up to date by itself. This page is for somebody who does not have it yet.
BOS Online is the same program with the devices connected. It adds four things: