Yes you can use any installation with opensprinkler. Each valve has two wires, one ground and one positive. You hook up all the ground wires together and plug that into the COM on any controller (including opensprinkler). You then plug each positive wire into each station as you see fit. You can choose to combine a few valves if you have enough water pressure. This determines your “zones.”
You get web access by connecting the raspberry pi to your home wifi, and then by installing the opensprinkler program.
If you already have a system in place all you would need to do is disconnect the existing wires and plug them into the opensprinkler.