Yes, the QuickBooks Online app for mobile and desktop is for free.
Once you have already subscribed to one of the QuickBooks Online product, you can log in to the app and use it freely.
If you haven't subscribed to the QuickBooks Online system yet, you can use this link to get a specific product for a month free trial or have it three months discounted price:: QuickBooks Plans and Pricing.
Let me know if you have other concerns about the QuickBooks Online app. I'll keep this window open. Thanks for dropping by!