The app is free. You bring your own model: run one locally at no cost, or point it at a provider key you already pay for. There is no Zeph subscription to download the app.
No — the app runs on your Mac on its own. To put your agents on a screen you can talk to, Zeph drives a small compatible device: a Waveshare board today, with M5Stack and others coming soon.
macOS is first. Windows, Linux, and the iPhone and Android apps are on the way. No date to promise yet.