NoteDex is not free, but you can try it out for free for 7 days. You do not need to provide a credit card and you won't be billed unless you specifically purchase the app. After your 7 days trial the system will go into read only mode - so you can view any cards you create but you can't add any new ones.
How much does NoteDex cost?
NoteDex starts at $2.99/m if you pay monthly. You can save 30% if you purchase the annual plan. There is also a limited time offer of a lifetime deal for $49.
You can learn more about pricing options here https://www.notedexapp.com/plans-and-pricing