Whats the best nonogram website/app you recommend?

I just got into nonograms and i really like it. I'm looking for recommendations on apps you love the most. If you could please share the following:

1. What website/app is it
2. What platforms does it support
3. What do you love most about it
4. Is it single player only or multiplayer where i can play with my friends online?
5. Is it free or paid only? If paid, how much?