How to make an Ubuntu application integrated?

Question

I'm designing an application for Ubuntu and would like to make it feel natural and integrated in the OS. What are the available libraries, guidelines and frameworks that make an application look&feel native on an Ubuntu/Unity desktop? I don't exclusively mean GUI toolkits, but features like quicklists in Unity:

Answer 1

This page on the Ubuntu wiki is a good place to start. It lists a lot of the desktop integration tools and libraries.

Here are some of the important ones:

• AppIndicators - these are the indicators that sit in the tray
• Unity Lenses - the icons in your screenshot