Hello there,
The best I’ve found for app development is https://en.yeeply.com here all you need to is post your project with a description and then developers (who are registered to the website) will send you proposals, all you have to do is pick the right one for you (If you’re unsure you can ask their customer support very helpful). Once you’ve chosen your developer you pick and chose the tasks, how much time you want to spend on it and so forth, there is a chat system too, so you can stay in contact with your developer. The best part is that if you’re not happy with the developer’s work, you don’t have to pay a thing! hope that helps. Japanese Sword UK