It is possible, as I made a real-time chat project and in the project I was able to create, connect, and send messages from multiple instances of the project on the same machine. I think you just need to make a network server and client, and then pass information using Godot's network functions, like rpc. You could also potentially use Websockets, though I have not used it myself so I don't know how feasible it might be.
If you have not seen it already, the High Level Multiplayer section of the Godot documentation is a good reference. The Godot demo repository also has a bunch of networking demos that might be helpful.
Regardless, as long as you are okay with using Godot's networking stack to create a local server and passing data that way, then it should be possible for multiple Godot projects to communicate.
