I've been a Linux user for a while, and C++ programmer for a while longer. Is there a way to write applications for Ubuntu, and how to submit them?
To write applications for Ubuntu, you can use Quickly. It is for apps in Python and GTK. But you can also write applications with other frameworks that works on Linux (Qt for example).
All the informations that you need are on the Ubuntu Developer website : http://developer.ubuntu.com/