Ask HN: What is your best little-known paid mobile app?

I use Shapr 3D for making 3D models for printing. It's an iPad app, feels like I'm living in the future when I use that. Subscribed for about $200/year.

MoneyLover. Budgeting app. I didn't really need to pay for it, but after using it 3 years, I subscribed as a sort of donation.

V for wiki by raurief - love the app