What app do you wish existed for your online store?

[baakgwai]

I am a developer looking to generate some extra income. So, I am interested in knowing:

1. Are you currently using any 3rd party apps that you pay for?
2. If so, which apps are they?
3. Is there anything about any apps you have used that was annoying or caused issues?
4. Is there any functionality that you would pay to add to your store right now?

Thanks!