Nobe OmniScope Pro
Nobe OmniScope Pro comes as a subscription that is renewed yearly.

Do I need to renew the subscription to keep using the app?

No, once your subscription is expired you can continue using your current Nobe OmniScope version indefinitely. You will not be able to update to the versions released after your subscription expiration date.
The subscription cost covers the application updates and priority support (email and TeamViewer help) after one year.
The applications stays fully functional with the expired subscription status. It just cannot be updated to the latest version available.