In this list you can find many Arduino compatible circuits and projects that are Atmel and Non-Atmel based.
In this post, I'll show you an Arduino code compatible project that is based on PIC Microcontroller.
Pinguino is a project based on PIC Microcontroller from Microchip Manufacturer.
I'm a big fan of PIC microcontroller long before I knew Arduino. So once I knew about Pinguino I got excited to build it.
It supports a wide range of Microcontrollers including 8 and 32 Bits.
It has its own IDE but it's code compatible with Arduino.
This means that you can use the code written for Arduino in your own Pinguino projects.
You can find detailed instructions of how to build this circuit step-by-step on my instructables page and on my blog.
Source: My Instructables Page