Hey Felipe, this looks really clean. I'll give you some first impressions I had and hope they ate useful.

What is this app on? Is it just a website or is it a mobile app? Is it going to work offline?

What does "decorating cards" mean? I haven't heard that term before but it seems to be a key part of your selling point.

Also, how does adding variations to a card in your app differ to just adding variations as new cards in another app?

The screenshot of the app could be a lot bigger (Firefox mobile). There's two layers of blank space around so I can't actually read the text without zooming.

"Most apps use reverse cards (Q->A, A->Q)" I don't understand what this means.

I like the pricing scheme. It's simple. The only thing I would change is to add rent to buy. E.g. if you pay 20 for a year and then decide you want lifetime it's only 30. This helps to avoid the situation where 50 is too much for someone when they aren't sure they'll keep using it but 20 feels like a bad deal if they end up using it a lot and get the lifetime anyway (they've "wasted" 20).