The mobile app runs on iPhone, iPad and Android, and it is a full Grape rather than a companion viewer.
iPhone and iPad
The iOS app is on the App Store. Install it from the store listing linked on the download page. On iPad the app rotates freely, so it works in landscape and with a keyboard. Once it is in, your notes, folders, tags and chats also turn up in Spotlight when you search from the Home Screen.
Android
The Android app is on Google Play. Install it from the store listing linked on the download page like any other app.
The first open
No account, no setup. Grape creates a local library on the phone, adds a couple of sample notes, and shows a short welcome tour of the main features. Permissions are only requested when a feature needs them, like the microphone the first time you record.
Using it with the desktop app
Notes stay on the phone unless you turn on sync, which keeps the phone and the desktop app on the same library with a Sync or Pro subscription, or through your own Dropbox or Google Drive on Lifetime. Get started with Grape ends with exactly that: signing the phone in to the account you use on the computer.
New versions
The store handles updates here, so the app follows whatever you told your phone to do with them, and the first open after an update shows what changed. On a computer Grape updates itself instead.